global ice sheet system interlocked by sea level abstract denton and hughes 1983 quaternary research 20 125 144 postulated that sea level linked a global ice sheet system with both terrestrial and grounded marine components during late quaternary ice ages summer temperature changes near northern hemisphere melting margins initiated sea level fluctuations that controlled marine components in both polar hemispheres it was further proposed that variations of this ice sheet system amplified and transmitted milankovitch summer half year insolation changes between 45 and 75 n into global climatic changes new tests of this hypothesis implicate sea level as a major control of the areal extent of grounded portions of the antarctic ice sheet thus fitting the concept of a globally interlocked ice sheet system but recent atmospheric modeling results manabe and broccoli 1985 journal of geophysical research 90 2167 2190 suggest that factors other than areal changes of the grounded antarctic ice sheet strongly influenced southern hemisphere climate and terminated the last ice age simultaneously in both polar hemispheres atmospheric carbon dioxide linked to high latitude oceans is the most likely candidate shackleton and pisias 1985 atmospheric carbon dioxide orbital forcing and climate in the carbon cycle and atmospheric co2 natural variations archean to present e t sundquest and w s broecker eds pp 303 318 geophysical monograph 32 american geophysical union washington d c but another potential influence was high frequency climatic oscillations 2500 yr it is postulated that variations in atmospheric carbon dioxide acted through an antarctic ice shelf linked to the grounded ice sheet to produce and terminate southern hemisphere ice age climate it is further postulated that milankovitch summer insolation combined with a warm high frequency oscillation caused marked recession of northern hemisphere ice sheet melting margins and the north atlantic polar front about 14 000 14c yr b p this permitted renewed formation of north atlantic deep water which could well have controlled atmospheric carbon dioxide w s broecker d m peteet and d rind 1985 nature london 315 21 26 combined melting and consequent sea level rise from the three warming factors initiated irreversible collapse of the interlocked global ice sheet system which was at its largest but most vulnerable configuration

composition of characteristic soils on the raised atoll bellona solomon islands abstract knowledge is scarce about the composition of soils on bellona and other pacific atolls such knowledge is important as it is closely related to sustainable land use of these special soils formed on carbonatic phosphatic materials therefore the micromorphological chemical and mineralogical composition of samples from genetic horizons in three dominant bellonese soils malanga kenge ungi and kenge toaha and underlying rock tanahu were investigated tanahu mainly consists of dolomite but this mineral is absent in the three soils which are dominated by phosphate containing minerals the malanga soil is strongly dominated by ca and p with minor amounts of al f and fe present in fluorapatite hydroxyapatite and crandallite in contrast al fe and p dominate in the kenge ungi and kenge toaha soils in accordance with a mineralogy consisting of crandallite together with aluminum oxides gibbsite boehmite and iron oxides mainly goethite with minor contents of hematite the observed carbonate for phosphate substitution in the apatites and crandallite is important as it indicates an increased phosphate availability in the soils all three soil samples contain 1 si and very little k and mg total contents of essential microelements are considered adequate but the rather high contents of sr and u especially in the kenge ungi soil may be problematic although the composition of the soils suggests substantial fertility and resilience the lack of k containing weatherable minerals silicate minerals is in line with a very low k and low mg content and explains why fertilization may be needed to sustain future cultivation of these special soils due to a possible low bioavailability of fe mn and maybe other micronutrients at the circumneutral ph of these carbonatic phosphatic soils as well as the rather high contents of sr and u it may be recommended to test element availability using appropriate chemical soil tests supplemented by plant experiments to ensure safe and sustainable optimal soil use however according to the local farmers the malanga kenge toaha and kenge ungi soils are considered well suited for production of the preferred crops

paleoenvironmental implications of the guano phosphatic cementation on dongdao island in the south china sea abstract the phosphatic cement in the bioclastic sediment sequence on the northeastern shore of dongdao island in the south china sea was studied and its paleoenvironmental implications discussed petrological characteristics and major trace ree element data unequivocally supported the notion that phosphatization was closely associated with avian guano decomposition and leaching whereas carbon and oxygen isotope results further revealed that meteoric water were involved in these processes ams 14 c dates on the brown phosphate cements indicate that they were formed around 5700 5000 5100 and 2900 yr bp respectively the multi episodes of phosphatization very likely correspond to intermittent seabird occupation on this island possibly reflecting holocene sea level oscillation and or long term climate changes in the south china sea that have controlled seabird habitat the phosphate cementation which occurs widely in tropical islands may be another useful monitor for sea level and or paleoclimate changes

origin of atoll dolomites distinguished by geochemistry and crystal chemistry kita daito jima northern philippine sea abstract kita daito jima is a carbonate island located at the northwestern region of the philippine sea 25 55 6 57 6 n 131 16 9 19 8 e dolomites extend from the island surface to a depth of 100 m below the ground surface mbgs strontium isotope stratigraphy indicates that subsurface units c1 0 49 7 mbgs and c2 49 7 103 4 mbgs were dolomitized at 5 5 ma and 2 0 ma respectively and that island surface dolomites are products of dolomitization at 1 6 2 0 ma x ray diffraction analysis indicates that the island surface and borehole dolomites comprise variable mixtures of four and three dolomite crystal phases respectively each of these phases is distinguished by a different ca and mg content three textural types can be recognized in the kita daito jima dolomites fabric preserving crystalline nonmimetic cnm crystalline mimetic cm and fabric preserving microsucrosic ms cnm dolomites contain more calcian phases whereas ms dolomites commonly are richer in more stoichiometric phases backscattered electron images indicate that calcian dolomite phases were precipitated earlier than the more stoichiometric dolomite phases and that there is no significant hiatus between the phases although they are diachronous both the island surface and borehole cores dolomites show linear relationships between whole rock 18o composition and mg contents and between whole rock trace element concentrations sr and na and mg contents these covariances result from phase mixing not stoichiometric effects deconvolution of whole rock isotopic and elemental compositions based on the relative abundance of phases reveals that each phase has a distinct chemical and isotopic composition oxygen isotopic compositions of the island surface and borehole dolomites suggest that all dolomite phases formed in seawater and that dolomitization primarily occurred during glacio eustatic sea level lowstands and cooler ocean temperatures

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

an occurrence of cadmiferous phosphorite soil concretions in jamaica abstract bauxite exploration drilling revealed the presence of phosphate minerals through the chemical and xrd analysis of recovered drill hole samples at spitzbergen in manchester parish jamaica a subsequent pit led to the discovery of phosphorite concretions composed of hard competent masses of finely crystalline fluorapatite with some minor crandallite the phosphorite contains anomalously high levels of zn 5000 mg kg 1 cd 1 1 ag 20 mg kg 1 be 80 mg kg 1 and to a lesser extent u textural and geochemical evidence indicates that the phosphorite concretions were most likely formed by the replacement of limestone by secondary deposition proximal to fossil guano deposits postulated to be late miocene or pliocene sea bird colonies mechanical dispersion of the phosphorite concretions through karst weathering processes has led to their wider spatial distribution than the original guano deposits subsequent weathering of the concretions and the admixture of their decomposition products into the bauxitic and terra rossa soils is postulated to be the cause of the widespread anomalous levels of zn cd and be in these soils in central jamaica and the elevated levels of p in the bauxite

oxygen isotopes of phosphate and the origin of island apatite deposits abstract in an attempt to test the hypothesis that insular phosphorites on high islands e g nauru formed by chemical reactions between seabird guano and carbonate the oxygen isotope compositions of phosphate 18op in modern guano and in the apatite component of phosphorites of various ages and locations have been investigated guano from several species of seabird appears to have 18op values that are in equilibrium with the ambient seawater temperature at each site however recent apatites closely associated with modern guano can have 18op values that are as much as 2 higher than their inferred guano phosphate source this shift in 18op values could be the result of isotopic re equilibration with percolating meteoric waters which have been enriched by evaporative processes in the upper part of the soil profile bacterial degradation of the guano in the soil zone is a possible mechanism for resetting the 18op values in this environment ancient apatites on high islands such as nauru ocean island and makatea have 18op values that are significantly lower than the 18op values of recently formed apatites the results indicate that ancient apatite deposits could not have formed by processes similar to those forming recent apatites without unreasonably high palaeotemperatures and or equilibration with water with much lower 18o values such as meteoric water in a karstic terrain at the time of maximum infiltration if the 18op values in apatite are subject to modification during subaerial weathering and diagenesis perhaps aided by the metabolic activity of micro organisms the application of 18op signatures of insular phosphorites to palaeoenvironmental reconstructions is limited to post depositional history and provides few clues to original setting

the cycle of phosphorus in an atoll ecosytem the major subsystems of an atoll relevant to the phosphorus cycle are the sea 0 015 g t p and atmosphere the marine biosphere 103g t p the supramarione portion of the atoll s carbonate substrate including rock and soils 103g t p the freshwater lens contained in that substrate 7 102g t p and terrestrial flora and fauna by way of example among low islands of tuvalu vegetation principally coconut palms contains 0 5t ha p while people pigs and minor fowl account for about 2 5 3 kg ha p the sea is the primary source and sink for phosphorus in an atoll ecosystem with the primary concentration taking place in the marine biosphere 1 2kg ha m a p and subsequent transference to the land by physical geological processes 104 g t a p and terrestrial predators 1kg ha a p the freshwater lens has a central role in redistributing phosphate received from atmospheric fallout corrosion of bioclasts and breakdown of surface debris this phosphorus is transported through the calcareous substrate as a humate complex that breaks down in or near the vadose zone excess free phosphate is precipitated as dahllite carbonate hydroxyapatite removing it from further participation in the atooll s geochemical cycle phosphorus in the fresh groundwater is recycled in the terrestrial flora 0 1t ha a p or los in edge discharge the cycle of phosphorus offers a model for evaluating environmental impacts but data is presently insuffient to determine precise quantities being transferred within and between all the component subsystems of the atoll no satisfactory budget can be constructed detailing net losses and net inputs between different subsystems and hence likely effects of present land management practices thriving populations pollution and environmental changes the atoll is a highly dynamic system able to recover from short term environmental disruptions but its resilience in this regard needs to be carefully monitored quantified and nurtured

half a century of dynamic coastal change affecting mangrove shorelines of french guiana a case study based on remote sensing data analyses and field surveys the mobile mud banks several kilometres wide and about 30 km long which form the sedimentary environment of the coast of the guianas are a consequence of the huge particulate discharge of the amazon these mud banks shift towards the northwest influenced by the combined action of accretion and erosion a process also affected by periodic variability because of this movement the coastline is unstable and continuously changing such changes determine the structure and composition of mangrove forests the only type of vegetation adapted to this dynamic environment the objectives of this study were to identify coastal changes that took place over the last 50 years and to relate them to natural processes of turnover and replenishment of mangrove forests these objectives have been achieved through a combination of remote sensing techniques aerial photographs and spot satellite images and field surveys in the area of the sinnamary estuary french guiana ground data were collected in representative mangrove forest stands chosen as a function of their growth stages and their structural features from pioneer and young stages to adult mixed and declining formations the coastline changes and the mangrove dynamics over the 1951 1999 period are analyzed through production of synthetic digital maps showing an alternation of net accretion 1951 1966 and erosion periods 1966 1991 followed by the present accretion phase based on this structural functional and historic information a global scenario of mangrove forest dynamics is proposed including a model of forest development forest gap processes and sedimentological dynamics the results of this research are discussed within the context of regional coastal amazonian area and global climate d 2004 elsevier b v all rights reserved

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

chenier plain development in northern sierra leone west africa abstract the coast of northern sierra leone between the scarcies and mellacoree estuaries forms a prograding muddy holocene plain comprising two separate as yet undated clusters of sand cheniers the general coastal morpho stratigraphy and available data on regional climatic and sealevel history suggest that alternations between muddy progradation and chenier cluster formation have been controlled by a probable conjunction of several factors including the local geomorphic framework a climatically induced change in mud supply and relative sealevel oscillations since the middle holocene the inner chenier cluster was apparently elaborated under conditions of efficient wave action over a deep largely unfilled mellacoree estuary and at a time of reduced mud availability it peters out seaward probably in response to several factors including an increase in mud supply from the upland a negative sealevel pulse resulting in higher rates of mud export from accreted inner tidal flats increased muddy sedimentation over a shallower nearshore zone and attenuated wave action as a result of energy capture by accreted estuarine shoals the outer cluster which partly fringes the coast was formed in a mayor embayment representing the terminus of longshore sand drift it is suggested that its formation may have been favoured by a higher sealevel resulting in efficient winnowing of sands from subtidal muds a greater propensity for accretion of tidal flats landwards and consequently a lower mud supply to the foreshore although the timing of muddy progradation and chenier formation has not been determined the foregoing interpretation suggests a complex sequence of events reflecting as much the influence of local morphodynamic factors as external factors

sedimentation in a fluvially infilling barrier bound estuary on a wave dominated microtidal coast the oueme river estuary benin west africa the oueme river estuary is located on the seasonally humid tropical coast of benin west africa a striking feature of this microtidal estuary is the presence of a large sand barrier bounding a 120 km2 circular central basin lake nokoue that is being infilled by heterogeneous fluvial deposits supplied by a relatively large catchment 50 000 km2 borehole cores from the lower estuary show basal pleistocene lowstand alluvial sediments overlain by holocene transgressive highstand lagoonal mud and by transgressive to probably early highstand tidal inlet and flood tidal delta sand deposited in association with non preserved transgressive sand barriers the change in estuary mouth sedimentation from a transgressive barrier inlet system to a regressive highstand barrier reflects regional modifications in marine sand supply and in the cross barrier tidal flux associated with barrier inlet systems as barrier formation west of the oueme river led to an increasingly rectilinear shoreline the longshore drift cell matured ensuring voluminous eastward transport of sand from the volta delta in ghana the major purveyor of sand to the oueme embayment 200 km east concomitantly the number of tidal inlets and the tidal flux associated with a hitherto interlinked lagoonal system on this coast diminished complete sealing of lake nokoue has produced a large permanently closed estuary where tidal intrusion is assured through the interconnected coastal lagoon via an inlet located 60 km east since 1885 tides have entered the estuary directly through an artificial outlet cut across the sand barrier although precluding the seaward loss of fluvial sediments permanent estuary mouth closure has especially deprived the highstand estuary of marine sand a potentially important component in estuarine infill on wave dominated coasts in spite of a significant fluvial sediment supply estuarine infill has been moderate because of the size of the central basin estuarine closure has resulted in two co existing highstand sediment suites with limited admixture the marine derived estuary mouth barrier and upland derived back barrier sediments this situation differs from that of mature barrier estuaries characterized by active fluvial marine sediment mixing and facies interfingering

depositional model of a macrotidal estuary and floodplain south alligator river northern australia the south alligator river northern territory of australia has a macrotidal estuary tidal influence spring tidal range 5 6 m at the mouth extends 105 km up the channel it is dominated by freshwater in the wet season december april with a salt wedge near the mouth but is well mixed and becomes saline throughout the dry season the tidal channel can be divided into four different channel types an estuarine funnel a sinuous meandering segment a cuspate meandering segment in which the inside of bends are pointed and an upstream tidal channel the distribution of morphologically defined land classes and morphological units within each land class on the floodplain flanking the estuary differs from one channel type to another several stratigraphic and morphostratigraphic units have been recognized from drill holes on the coastal and deltaic estuarine plains and a model of development is proposed on the basis of extensive radiocarbon chronology and palynology the coastal plain has prograded with most rapid sedimentation between 5000 and 3000 yr bp a similar pattern of progradation is identified in the estuarine funnel in the sinuous segment of the estuary the channel has migrated laterally across the floodplain previous channel positions are indicated by palaeochannels and the meander tract is occupied by laminated channel sediments within the cuspate segment there are numerous sinuous palaeochannels on the plains in the upstream segment the channel and palaeochannels have long straight reaches with irregular bends and discontinuous levees and channel avulsion is indicated mangrove mud is a widespread stratigraphic unit throughout the plains the initial phase of development is a transgressive phase 8000 6800 yr bp when mangrove forests extended landwards into a pre existing valley as sea level rose as sea level stabilized the transgressive phase was followed by a widespread mangrove phase termed the big swamp 6800 5300 yr bp the mangrove forests disappeared from most of the plains as vertical accretion continued and were replaced by grass and sedge covered floodplains during the sinuous phase about 5300 2500 yr bp the channel migrated laterally and eroded the deltaicestuarine plain and deposited lateral accretion deposits laminated channel sediments part of the channel of the south alligator river has then progressed from sinuous to cuspate in form and erosion of river banks has occurred transgressive and big swamp phases occurred under rising and stabilizing sea level respectively later morphodynamic channel adjustments occurred under conditions of stable sea level the depositional model has direct application to other estuaries in northern australia and may be applied to other areas where sea level change has been similar

groundwater flow in the bashita minato mangrove area and its influence on water and bottom mud properties in the bashita minato mangrove lagoon in iriomote island japan the following parameters were measured from 1985 to 1988 the groundwater level in the shore bank between the lagoon and the open sea the water levels in the lagoon and the open sea the water properties near the bottom and chlorophyll in the bottom soil of the lagoon the movement of groundwater depends on the soil characteristics and the difference in water levels in the lagoon and in the ocean and flows towards the lagoon modulated by the tidally reversing flow with exponentially dampened amplitude and linearly delayed phase the groundwater movements cause inflow and outflow with the tidal cycle through the bottom of the lagoon the momentum of the inflowing water mixes the bottom water with the overlying water resulting in dismantlement of the anoxic condition in the bottom layer at the tidal period the benthic algae photosynthesizing on the bottom sediment are entrained in the mud by the outflow of the lagoon water through the bottom layer the groundwater flow appears to play an important role in determining the water properties and the sediment condition of the mangrove area

a spatial analysis of the relationship between mangrove avicennia marinavar australasica physiognomy and sediment accretion in the hauraki plains new zealand the relationship between mangrove avicennia marina var australasica physiognomy and forest bed accretion was quantified using experimental and field measurements at the piako river mouth firth of thames new zealand sediment accretion under six densities of artificial pneumatophores was monitored for 13 weeks in an experimental plot while accretion was simultaneously monitored for 5 months at 102 locations along two parallel 500 m transects experimental results demonstrated that accretion increases with pneumatophore density this was supported by bivariate analyses of cumulative accretion and avicennia marina stem density basal area and pneumatophore density along the transects only the latter is significantly correlated with accretion geostatistical analyses showed that variation in sediment accretion occurs at the same spatial scale as pneumatophore density accretion and pneumatophore density are spatially autocorrelated over distances 70 m and have fractal dimensions of 1 5 1 6 it is proposed that avicennia marina grow pneumatophores at a density that balances the benefits of aeration with the drawbacks of sediment accretion these results are compared with the concept of positivefeedback switches in plant communities 1996 academic press limited

studies of a mangrove basin tuff crater new zealand iii the flux of organic and inorganic particulate matter abstract water samples were collected at 15 min intervals over 11 tidal cycles from a tidal creek draining the mangrove covered basin of tuff crater auckland new zealand the samples were filtered and total suspended sediment tss inorganic suspended sediment iss and organic suspended sediment oss were determined variation in tss was high the concentration varied over a tidal cycle and during over bank flows concentrations were lowest at or near slack high water covariance between tss concentrations and velocity and discharge meant that the calculation of particulate matter flux over tidal hemicycles was particularly dependent on the method of estimating tidal flux the hypsometrically based volumetric method was found to be inappropriate predicting a positive budget import more often than observed instead particulate matter budgets were calculated by means of the velocity area method and indicate a net export of tss iss and oss floating macrodetritus was observed on both the flood and ebb tides but a net export was found on the two tides monitored it is considered that on an annual basis floating macrodetritus export accounts for less than 2 of the detrital production in the basin and organic suspended sediment export from the basin is less than 3 kg c ha 1 day 1 and is below the rate of detrital production it is implied that a proportion of the organic detritus produced in this basin is degraded and recycled in situ

links between physical chemical and biological processes in bashita minato a mangrove swamp in japan bashita minato in iriomote island japan is a mangrove swamp separated from a coral reef slightly offshore by a sill made of coral sand as a result of storm dominated formation and erosion of the sill the water properties in the swamp vary widely with time when water flows over the sill into the swamp from a nearby coral reef at flood tide the oxygen cycle and the water properties in the swamp depend on both the semi diurnal tidal flows and the diurnal cycle of oxygen concentration in reef waters which is caused by biological activities i e photosynthesis and respiration in the shallow coral reef area when the entrance is blocked by the sill the swamp becomes ponded and the water temperature increases rapidly 1 c day 1 with a temperature maximum at a mid water layer as in a solar pond the bottom layer rich in organic matter from decaying mangrove detritus becomes anoxic within a day after the sill closure various chemicals are then released from the bottom mud the irradiance extinction coefficient increasing by as much as 1 m 1 day 1 this in turn results in continuous degradations in photosynthetic activity of benthic algae and in water properties until the sill is breached again under spring high tides or intense rainfall

studies of a mangrove basin tuff crater new zealand i mangrove biomass and production of detritus abstract the mangrove avicennia marina var resinifera in a tidally flooded explosion crater tuff crater near the southern latitudinal limit of mangroves in new zealand adopts two distinct growth forms taller tree like mangroves up to 4 m tall along the banks of the tidal creek and low stunted shrub mangroves less than 1 m tall on the mudflats twelve trees were felled and on the basis of a biomass height relationship for the taller trees and a biomass canopy width relationship for the lower above ground biomass excluding pneumatophores was estimated average above ground biomass for the taller mangrove was estimated to be 104 1 t ha 1 and for the lower 6 8 t ha 1 while the value for the taller mangroves is similar to figures reported for more complex tropical mangroves the fact that 94 of the basin is covered by low generally sparse mangroves means that total biomass for the basin is estimated to be 153 t an average of only 7 6 t ha 1 litter fall beneath the taller mangroves is estimated as 7 6 2 5 t ha 1 a 1 and beneath the lower mangroves 3 3 0 5 t ha 1 a 1 the value for the taller mangroves is similar to that reported from mangroves in many other parts of the world but because of the extensive low sparse mangroves the total for the basin is estimated as 53 7 t a 1 an average rate of 2 7 t ha 1 a 1 a very low rate of litter fall when compared with elsewhere decomposition of mangrove leaves occurs relatively rapidly with leaves losing half their dry weight in 10 weeks and then continuing to degrade but at a slower rate substrate sediment samples contain high organic matter content and although some organic matter appears to be exported via the tidal creek a proportion of the detrital production is evidently recycled in situ

the role of high energy events hurricanes and or tsunamis in the sedimentation diagenesis and karst initiation of tropical shallow water carbonate platforms and atolls abstract karst morphology appears early even during carbonate sediment deposition examples from modern to 125 ka old sub inter and supratidal sediments are given from the bahamas atlantic ocean and from tuamotuan atolls southeastern pacific ocean with mineralogical and hydrological analyses karstification is favoured by the aragonitic composition of bioclasts coming from the shallow marine bio factory lithification by aragonite cements appears as a rim around carbonate deposits and dissolution and non cementation start at the same time on modern supratidal deposits andros micrite or atoll coral rudite and provoke the formation of a central depression on small or large carbonate platforms in fact this early solution of the centre of platforms is closely related to the location of each of the studied examples on hurricane tracks high energy events such as hurricanes and tsunamis affect sediment transport but hurricanes also affect diagenesis as a result of the enormous volume of freshwater carried and discharged along their paths this couple lithification solution is localised at sea level and accompanies sea level fluctuations along the eustatic curve because of the precise location of hurricane action all around the earth early karstification by aragonite solution cementation and supratidal carbonate sediment accumulations high energy trails act together on all the platforms and atolls located inside the tropics 23 27 between roughly 5 10 and 25 on both hemispheres however early karstification acts alone on shallow carbonate platforms including atolls along the equatorial belt between 5 10 n and 5 10 s these early steps of karstification are linked to the ocean atmosphere interface due to the bathymetrical position of shallow carbonate platforms including atolls they lead to complex karstified emerged platforms called high carbonate islands where carbonate diagenesis together with the development of bauxite and or a phosphate rich cover and phreatic lens will occur

sediment dynamics and morphological stability of estuarine mangrove swamps in sherbro bay west africa abstract the relationship between the circulation of fine suspensions in a mangrove colonised estuarine complex short term mangrove substrate accretion and medium term mangrove swamp geomorphic evolution was studied in sherbro bay an infilling microtidal to mesotidal embayment in southern sierra leone formed behind holocene sandy beach ridge barriers the estuarine reaches of streams debouching into the bay have relatively high suspension concentrations sc of silts and clays that ranged during the survey period in 1991 from 0 8 to 40 g l 1 in association with the constitution of turbidity maxima 5 50 g l 1 at the interface between freshwater drainage and the saltwater intrusion however the surveyed mangrove swamp plots showed much lower suspension concentrations 0 09 0 6 g l 1 and low albeit minimum rates of accretion 1 1 3 mm a 1 monitored between 1980 and 1989 these low rates are attributed mainly to the short duration of tidal flooding due to a high substrate elevation within the tidal range and to the low settling potential of the very fine grained suspensions circulating over the swamps a comparison of two sets of aerial photographs 1954 1960 and 1976 showed that these swamps and their channel networks are also characterised by a remarkable medium term morphodynamic stability this stability and the low accretion suggest that the swamps and their channel networks are largely in equilibrium with the hydrology notably flooding duration and sediment loads settling out of mud from the turbidity zones contributes to higher accretion rates up to 12 mm a 1 not taking into account the effects of shallow subsidence on parts of the mudflats fronting the mangroves which are flooded for longer periods some of the mud is deposited over sandy channel bars in the main bay channel and the rest exported seaward it is tentatively suggested that an increase in the duration of tidal flooding generated by global sea level rise at the presently predicted rates could lead to higher sedimentation in the mangrove swamps thus enhancing accretion and the chances of mangrove survival

studies of a mangrove basin tuff crater new zealand ii comparison of volumetric and velocity area methods of estimating tidal flux abstract two methods which have been used in a number of studies of fluxes in salt marsh ecosystems direct measurement by velocity area estimation and hypsometrically based volumetric simulation have been compared for calculating tidal flux in tuff crater tuff crater a mangrove filled old volcanic explosion crater in the waitemata harbour new zealand has a physiography particularly suitable for such a study receiving minimal freshwater input having clearly defined boundaries and with all tidal exchange occurring via the tidal creek the topography of the basin was levelled contouring at 5 cm intervals with additional survey of creek cross sections and a volume stage curve was drawn discharge was estimated by changes in volume related to stage observations at the mouth of the basin direct measurement of flow was made at the gauging station by determining velocity at 0 2 0 6 and 0 8 of the water depth and multiplying by cross sectional area comparison of discharge time curves using the two techniques reveals a similar pattern of discharge over time with peak ebb discharge exceeding peak flood discharge and peaks reaching similar values using the two techniques however the volumetrically modelled discharge predicted an earlier reversal of the tide and an earlier ebb peak discharge it is implied that the water surface is not horizontal at all tidal stages and that water surface slopes develop on the ebb tide resulting from inertial effects in restricted channels and on the mangrove covered mudflats the volumetric model is therefore inappropriate for the calculation of tidal flux especially where this is used to calculate budgets of sediment or organic matter the velocity area method estimates discharges in excess of those predicted volumetrically the disparity probably results from estimating discharge using only one station in the cross section and is similar to errors of estimating discharge observed in other studies