stable nitrogen isotopes in angola basin surface sediments abstract sedimentary 15n contains a record of biogeochemical processes occurring in the water column stable nitrogen isotopes were measured in the bulk sedimentary matter of 18 surface sediment samples collected in three transects in the eastern angola basin perpendicular to the coast at 6 s 12 s and 17 s and two samples from the zaire estuary relative enrichment in 15n in sediments with distance from the coast was seen in each of the three transects off northern middle and southern angola values in the zaire fan northern angola and southern angola increased by 1 9 and 1 6 respectively from shallow 100 m to deep 4500 m water sediments and in middle angola by 2 5 water depth range 73 3809 m we propose that in the angola region the degree of fractionation of nitrogen isotopes in organic matter is a function of nutrient supply to sunlit waters the shift towards lighter isotopic values in shallow water signifies that the larger nitrate pool is not utilized as extensively as in water farther away from the coastal upwelling centers southern angola sediments were more than 1 lower average 15n 5 4 than the middle and northern transects average 15n 7 2 and 6 5 respectively this difference is attributed to higher nitrate concentrations in the surface water at 17 s for which there are two reasons one is that these sediments are located south of the angola benguela front at 16 s which demarcates the convergence of warm equatorial water with cold nutrient rich benguela current water the second cause is the intense namibian coastal upwelling zone extending northward up to the front comparisons of bulk 15n with 13corg and c n ratios show that the observed sedimentary 15n variations with water depth are due neither to water column diagenesis nor to mixing of terrestrial material with marine derived organic matter the two estuary sediment samples were mainly terrigenous in origin based on 13corg and c n ratios 15n values of these two samples were 7 0 and 7 6

distribution and sources of bulk organic matter om on a tropical intertidal mud bank in french guiana from elemental and isotopic proxies the mobile french guiana coast is a shoreface region downdrift of the amazon river where enormous quantities of inorganic and organic materials are exchanged with the atlantic ocean the rapid accumulation of these materials forms highly unstable shore attached mud banks which can be temporally emerged and then rapidly colonized and stabilized by microphytobenthos and opportunistic mangroves i e avicennia germinans mud banks are preferential sites for the accumulation and significant remineralization of organic matter om due to intense erosion deposition cycles and potential biological colonization the distribution and sources of bulk sedimentary om were characterized by elemental and isotopic analyses of four sediment cores together with samples from three potential om sources mangrove plants suspended particulate matter spm and microphytobenthos all collected from the landward face of the macouria mud bank french guiana total organic carbon toc and nitrogen tn concentrations in the sediment cores showed that om sources were characterized by spatio temporal variations in this mud bank the relative contributions of mangrove plants spm and microphytobenthos were estimated using a three end member mixing model based on tn toc atomic ratios and 13c values sedimentary om is mostly controlled by spm associated with variable amounts of om derived from mangrove plants and microphytobenthos these variations could be explained by topography and bed elevation which decrease submersion time and increase desiccation higher contributions of microphytobenthos are associated with black om rich laminae identified in sedimentary cores and linked to temporal emersion phases of the mud bank which favor the growth of benthic microalgae this result is confirmed by the calculation of the average sediment accumulation rate around 36 7 14 8 cm yr 1 taking into account the emersion of the study site every spring tide a fortnightly cycle this value is within the range of the previous results from other mud banks in french guiana but is more than ten times greater than values generally obtained in other coastal contexts

terrestrial organic carbon accumulation on the amazon deep sea fan during the last glacial sea level low stand abstract sediment cores from the amazon deep sea fan recovered during r v meteor cruise 16 2 show in detail the modern areal distribution of sedimentary organic carbon stable organic carbon isotopes of the organic matter om as well as variations in the depositional processes in addition we studied up to 300 m long drilled sediment records recovered during odp leg 155 which allow evaluation of temporal variations on the amazon fan our results reveal new evidence for a very rapid change of fan depositional processes and organic carbon source at times of sea level change over the middle and lower amazon fan to estimate the amount of terrestrial organic carbon stored in sediments from the last glacial in the amazon fan we used stable organic carbon isotopes of the om 13 c org organic carbon content corg and age models based on oxygen isotopes faunal data and magnetic excursions following our results the organic carbon accumulation on the amazon deep sea fan is controlled by glacio eustatic sea level oscillations interglacial sea level high stand sediments are dominated by marine om whereas during glacial sea level low stands terrestrial organic carbon is transported beyond the continental shelf through the amazon canyon and deposited directly onto the amazon deep sea fan glacial sediments of the amazon fan stored approximately 73 1015 g terrestrial corg in 20 000 years or 3 7 1012 g terrestrial corg yr 1 equivalent to 7 12 of the riverine organic carbon discharge assuming constant paleo discharge which is about the same amount of terrestrial organic carbon as deposited on the amazon shelf today 3 1 1012 g terrestrial corg yr 1 or 6 10 of the modern riverine organic carbon discharge

sulfate reduction related to the early diagenetic degradation of organic matter and black spot formation in tidal sandflats of the german wadden sea southern north sea stable isotope 13c 34s 18o and other geochemical results abstract a stable isotope geochemical investigation 34 s 32 s 13 c 12 c 18 o 16 o has been carried out to study the development of anoxic surface sediments black spots in the backbarrier tidal area of spiekeroog island southern north sea microbial sulfate reduction related to the degradation of mainly marine organic matter under anaerobic conditions led to the accumulation of hydrogen bisulfide up to 8 mm in the interstitial waters of the sandy sediments while the carbon isotopic composition of organic matter reflected the downcore preferential degradation of labile marine organic matter sulfur and oxygen isotope variations in the dissolved sulfur species provided information about the microbiologically mediated complex interactions between the sulfur carbon and oxygen cycles

a review of coastal palaeoclimate and relative sea level reconstructions using δ13c and c n ratios in organic material holocene reconstructions of relative sea level rsl and environmental change in the coastal zone have become progressively more numerous since the importance of assessing possible future sea level rises has become apparent traditionally this has been achieved using a combination of biological and physical indicators e g pollen diatoms foraminifera grain size etc in some circumstances microfossils can be rare or absent from holocene sediments and in these cases carbon isotope ratios 13c and organic carbon to total nitrogen ratios c n can be used because they have the potential to provide information as to the origin of organic material preserved in coastal environments the distinction in 13c and c n of the various sources of carbon to estuarine sediments has led to its wide use as a tracer of carbon pathways and storage in estuaries more recently these techniques have been applied to holocene sediments to decipher changes in palaeocoastal environments and thus position relative to sea level and or palaeoriver discharge which have direct relevance to palaeoclimate this paper reviews the studies that have utilised this technique and explores examples from a wide range of coastal environments saltmarshes estuaries lagoons isolation basins and fjords it also discusses the potential alteration of geochemical signatures as a result of decompositional processes organic matter decomposition has been shown to change sediment 13c and c n values and thus an understanding of the processes involved is necessary in order to have confidence in the palaeoenvironmental interpretation of holocene 13c and c n decompositional shifts in c n and particularly 13c can occur over a relatively short time period however it is the direction of change in 13c and c n rather than absolute values that is key for interpreting changes in relative sea level and thus such changes are commonly preserved

the composition of sedimentary organic matter in relation to the dynamic features of a mangrove fringed coast in french guiana the sedimentary organic matter content of a series of 2 m deep cores was examined in relation to the evolution of mangrove forest on the basis of geochemical analyses and optical observations avicennia dominated forest deposits developing along the highly dynamic coastline of french guiana were collected in five stations based on stage of forest evolution the sedimentary organic matter in the upper sediment of the youngest mangrove swamp is mainly derived from algal mats with low carbon nitrogen ratios c n ratio from 6 to 8 and typical greyish amorphous organic flakes as observed in optical studies indeed rare young avicennia trees are present and effectively geochemical parameters do not give evidence of a litter made up of higher plant debris these rare debris being probably exported by the tides a slight increase with depth in the first decimetres of both total organic carbon toc content and c n ratio results from the development of the radial cable root system of the pioneer avicennia germinans early diagenetic conditions of this young forest are rather controlled by dominant suboxic processes as suggested by high eh values range 200 400 mv and local anoxic processes occurrence of pyrite in micro environments this is mainly due to the oxygen available by roots and crab bioturbation the organic content of the senescent mangrove sediment is mainly derived from higher plant debris in the uppermost 30 cm as indicated by relatively high c n ratios and the predominance of ligno cellulosic debris the strong decrease in hydrogen index values results from the degradation of the higher plant debris losing hydrogen bounds through decay processes moderately acidic ph values low ehs and the presence of pyrite framboids point towards the reducing decay processes in surficial layers of the senescent mangrove mediated by sulphate reducing bacteria whatever the stage of evolution of the forest the geochemical characteristics of the sediment below 30 cm are those of the shoreface one with opaque refractory debris derived from the amazon river detritus discharge the sediment collected from dead mangrove forests subsequently recolonized by pioneer mangroves contains organic markers which predate recolonization recording previous phases of erosion and accretion

the landsat image mosaic of antarctica abstract the landsat image mosaic of antarctica lima is the first true color high spatial resolution image of the seventh continent it is constructed from nearly 1100 individually selected landsat 7 etm scenes each image was orthorectified and adjusted for geometric sensor and illumination variations to a standardized almost seamless surface reflectance product mosaicing to avoid clouds produced a high quality nearly cloud free benchmark data set of antarctica for the international polar year from images collected primarily during 1999 2003 multiple color composites and enhancements were generated to illustrate additional characteristics of the multispectral data including the true appearance of the surface discrimination between snow and bare ice reflectance variations within bright snow recovered reflectance values in regions of sensor saturation and subtle topographic variations associated with ice flow lima is viewable and individual scenes or user defined portions of the mosaic are downloadable at http lima usgs gov educational materials associated with lima are available at http lima nasa gov

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

comparison of different retrieval techniques for melt ponds on arctic sea ice from landsat and modis satellite data melt ponds are regularly observed on the surface of arctic sea ice in late spring and summer they strongly reduce the surface albedo and accelerate the decay of actic sea ice until now only a few studies have looked at the spatial extent of melt ponds on arctic sea ice knowledge of the melt pond distribution on the entire arctic sea ice would provide a solid basis for the parameterization of melt ponds in existing sea ice models due to the different spectral properties of snow ice and water a multispectral sensor such as landsat 7 etm is generally applicable for the analysis of distribution an additional advantage of the etm sensor is the very high spatial resolution 30 m an algorithm based on a principal component analysis pca of two spectral channels has been developed in order to determine the melt pond fraction pca allows differentiation of melt ponds and other surface types such as snow ice or water spectral bands 1 and 4 with central wavelengths at 480 and 770 nm respectively are used as they represent the differences in the spectral albedo of melt ponds a landsat 7 etm scene from 19 july 2001 was analysed using pca the melt pond fraction determined by the pca method yields a different spatial distribution of the ponded areas from that developed by others a modis subset from the same date and area is also analysed the classification of modis data results in a higher melt pond fraction than both landsat classifications

sea ice albedo climate feedback mechanism abstract the sea ice albedo feedback mechanism over the arctic ocean multiyear sea ice is investigated by conducting a series of experiments using several one dimensional models of the coupled sea ice atmosphere system in its simplest form ice albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature further decreasing the areal cover of snow and ice it is shown that the sea ice albedo feedback can operate even in multiyear pack ice without the disappearance of this ice associated with internal processes occurring within the multiyear ice pack e g duration of the snow cover ice thickness ice distribution lead fraction and melt pond characteristics the strength of the ice albedo feedback mechanism is compared for several different thermodynamic sea ice models a new model that includes ice thickness distribution the ebert and curry model the maykut and untersteiner model and the semtner level 3 an

biogeochemical properties of water in surface ponds on antarctic fast ice and their relationship with underlying sea ice properties surface ponds on antarctic fast ice were examined by measuring temperature salinity and concentrations of chlorophyll a chl a dissolved inorganic carbon dic and nutrients no3 no2 po4 and sio2 in the surface pond water and under ice water sea ice cores were also collected from the bottom of a surface pond pond ice core and from a site away from the pond bare ice core time series measurements of surface pond water temperature showed that it varied with solar radiation rather than with air temperature comparison of water properties between surface pond water and under ice water suggested that dic and nutrients were consumed by biological productivity during pond formation depth profiles of nutrient concentrations in the pond ice core suggested the remineralization of organic matter at the bottom of the surface pond the chl a concentration was lower at the bottom of the pond ice core than in the bare ice core suggesting that surface pond formation reduces ice algae abundance in sea ice because meltwater flushes algae from the porous sea ice into the under ice water

comparison of aerial video and landsat 7 data over ponded sea ice the development of melt ponds on arctic sea ice during spring and summer is of great importance to the arctic climate system as it accelerates the decay of the sea ice and greatly reduces the albedo both melt pond development and its spatial distribution are needed to understand the surface energy balance in summer previously a technique was developed for classifying summer sea ice characteristics including the amount of open water white snow covered ice wet ice and melt ponds using landsat 7 enhanced thematic mapper plus etm spectral information in this paper we refine this technique through the use of airborne video data coincident with landsat etm imagery obtained over baffin bay on june 27 2000 the video images having a resolution of about 1 5 m at an aircraft altitude of 1 4 km are classified into open water ponded or wet ice and unponded sea ice comparison of the video and landsat imagery shows that many of the melt ponds are too small to cover an entire landsat pixel resolution of 30 m so that the landsat classification scheme would underestimate melt pond fraction thirteen high resolution video images are classified to develop a method to calculate fractions of open water ponded or wet ice and unponded ice from landsat 7 data a comparison between these classified video images and landsat retrievals yields a correlation coefficient of 0 95 with rms errors of less than 9 for the two ice types and 2 for open water comparisons of landsat and video analyses not used in the development of the algorithm yield correlation coefficients of 0 87 for open water 0 68 for ponded ice and 0 78 for unponded ice the rms differences are 10 8 and 11 respectively

coupling between sedimentary dynamics early diagenetic processes and biogeochemical cycling in the amazon guianas mobile mud belt coastal french guiana coastal french guiana lies within the vast mobile mudbelt that characterizes much of the s american inner shelf downdrift of the amazon river approximately 15 20 of the amazon sediment outfall moves nw along the guianas in part as a series of 20 25 coastal mud waves seasonal studies of a representative migrating mudwave located between kourou and sinnamary french guiana demonstrate that diagenetic properties and biogeochemical cycling are closely coupled to sedimentary dynamics and the refluxing of reduced components between the seabed coastal facies and well oxygenated overlying water an unsteady two zone diagenetic regime is typically present in the shallow subtidal and low intertidal regions a surficial layer usually 0 5 1 m thick is nonsulfidic highly reactive and dominated by fe mn cycling this suboxic layer unconformably overlies more consolidated sediment in which net so42 reduction is often observed and contracts shoreward toward the mangrove fringe as sediments stabilize and become bioturbated the relatively stable intertidal flats are also sites of significant benthic primary production despite suboxic conditions over extensive intervals anaerobic remineralization rates are high co2 0 2 0 6 mm day 1 and often show little evidence of attenuation with depth integrated co2 fluxes are 20 235 mmol m 2 day 1 wet dry season average 120 far exceeding diffusive o2 fluxes into the bottom high reactivity 0 08 day 1 and low c n remineralization release ratios 5 3 of decomposing material imply fresh substrate of marine origin most reduced solid phase fe is present as nonpyritic authigenic fe minerals 20 fe ii is in pyrite and low sedimentary c s ratios 6 8 reflect the generally nonsulfidic conditions a broad range of tracers e g 234th t1 2 24 days 210pb t1 2 22 years seasonal cl profiles and nonsteady state diagenetic models of pore water concentrations and oxidant reductant relationships demonstrate that the upper 0 1 1 m of deposits are reworked and exchanged with overlying water on timescales of 10 days to seasonally thus the seafloor acts as a massive suboxic batch reactor entraining and processing reactive marine plankton regenerating fe mn oxides exchanging metabolites and nutrients with the oxygenated water column and generating suites of nonsulfidic authigenic minerals the apparent paradoxical properties of high remineralization rate low reductant content corg 630 mol g 1 and dominance of suboxic metal cycling are a direct consequence of frequent entrainment of highly reactive organic substrate and simultaneous regeneration of the major fe oxidants in oxygenated water the amazon guianas mobile mudbelt is a zone of extraordinarily intense sedimentary and biogeochemical recycling greatly exceeding stable coastal systems such as salt marshes in material exchange with the sea

mixing mechanisms in cumulus congestus clouds part ii numerical simulations abstract the entrainment mechanisms of deep convective clouds in south africa are simulated by using both axially and slab symmetric cumulus models having very high spatial and temporal resolutions the simulated clouds on three different days show a structured organization with small scale features such as in cloud downdrafts the mixing processes are examined by analyzing the time variation of dynamic and thermodynamic quantities along computed parcel trajectories the calculations indicate that most of the entrainment occurs at the cloud top evaporative cooling and perturbation pressure cause downdrafts that transport highly diluted air from the cloud top down to lower levels the penetrative downdrafts are mainly located near the edges of the cloud in the presence of wind shear the downshear portion of the clouds becomes cooler and more diluted and it is associated with stronger downdrafts compared to the upshear side the asymmetric organization is attributed to turbulent exchange of horizontal mo

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

distribution and sources of particulate organic matter in the water column and sediments of the fly river delta gulf of papua papua new guinea suspended particles from surface and bottom waters and surficial sediments from the seabed were collected throughout the fly river subaqueous delta region during the monsoon season in january 2003 because of the unusually low river discharge associated with a strong el nino water column salinities were relatively high 10 to 32 throughout most of the delta with brackish salinities 4 wt relatively high organic carbon nitrogen molar ratios oc n 20 mol mol and quite depleted stable isotopic compositions of organic carbon 13coc 27 in contrast surface sediments in the seabed displayed spatially uniform compositions that were characterized by markedly lower oc contents 1 1 0 8 wt lower oc n ratios 17 9 mol mol and relatively enriched 13coc compositions 25 5 1 1 the radioisotopic compositions of oc from a selected set of seabed samples 14coc of 408 82 indicate om in surface sediments is old 14c ages of 2800 to over 6000 years before present the ratios of organic carbon to mineral surface area exhibited by these sediments are within the typical mono layer equivalent ranges characteristic of shelf sediments and do not reflect the preferential removal of terrigenous om overall these compositions indicate that while water column pom appears to be derived mainly from terrigenous vascular plant debris and riverine estuarine phytoplankton the source of most of the sedimentary pom is aged soil oc ultimately derived from c3 vegetation we speculate that the concentrations and sources of suspended pom in the water column of the fly river delta region reflect the conditions of low river discharge low wave energy and neap tides encountered at the time of sampling in contrast pom compositions in surface sediments are consistent with the transport and deposition of old mineral bound oc most likely eroded from the upland regions of the fly river watershed which is characterized by steep slopes high precipitation and c3 tropical forests and grasslands

organic matter budget in the southeast atlantic continental margin close to the congo canyon in situ measurements of sediment oxygen consumption abstract a study of organic carbon mineralization from the congo continental shelf to the abyssal plain through the congo submarine channel and angola margin was undertaken using in situ measurements of sediment oxygen demand as a tracer of benthic carbon recycling two measurement techniques were coupled on a single autonomous platform in situ benthic chambers and microelectrodes which provided total and diffusive oxygen uptake as well as oxygen microdistributions in porewaters in addition sediment trap fluxes sediment composition org c tot n caco3 porosity and radionuclide profiles provided measurements of respectively input fluxes and burial rate of organic and inorganic compounds the in situ results show that the oxygen consumption on this margin close to the congo river is high with values of total oxygen uptake tou of 4 0 6 3 6 0 5 mmol m 2 d 1 at 1300 and 3100 m depth respectively and between 1 9 0 3 and 2 4 0 2 mmol m 2 d 1 at 4000 m depth diffusive oxygen uptakes dou were 2 8 1 1 2 3 0 8 0 8 0 3 and 1 2 0 1 mmol m 2 d 1 respectively at the same depths the magnitude of the oxygen demands on the slope is correlated with water depth but is not correlated with the proximity of the submarine channel levee system which indicates that cross slope transport processes are active over the entire margin comparison of the vertical flux of organic carbon with its mineralization and burial reveal that this lateral input is very important since the sum of recycling and burial in the sediments is 5 8 times larger than the vertical flux recorded in traps transfer of material from the congo river occurs through turbidity currents channelled in the congo valley which are subsequently deposited in the lobe zone in the congo fan below 4800 m ship board measurements of oxygen profiles indicate large mineralization rates of organic carbon in this zone which agrees with the high organic carbon content 3 and the large sedimentation rate 19 mm y 1 found on this site the lobe region could receive as high as 19 mol c m 2 y 1 1 3 being mineralized and 2 3 being buried and could constitute the largest depocenter of organic carbon in the south atlantic

marine geology of the gulf of trieste northern adriatic geochemical aspects abstract geochemical analyses of surficial sediment in the gulf of trieste in terms of organic carbon total nitrogen and phosphorus 13c composition of sedimentary organic matter the trace metals hg pb cr cu zn cd ni mn and fe and the radionuclides 137cs and 210pb were carried out the higher values of organic carbon total nitrogen and phosphorus are restricted to the clayey silty sediments of the small bays of koper piran muggia and panzano and around the river isonzo outflow on the basis of 13c values the sedimentary organic matter is of entirely marine origin in the central part of the gulf which is bordered by two areas of greater terrigenous influence with the exception of hg and pb the areal distribution of the trace metals is similar to that of carbon nitrogen and phosphorus with higher contents in the clayey silty and silty sediments the mercury and pb contents exhibit a gradual decrease from the mouth of the isonzo river towards the southern part of the gulf riverine inputs also provide the most important sources of 137cs in the sediments of the gulf high 137cs activities in the uppermost layer of the cores indicate the chernobyl signal and in contrast to 210pb the vertical profiles show its occurrence in deeper layers which is attributed to diffusion of the 137cs distribution studies of the biogenic elements carbon nitrogen and phosphorus and the trace metals in the surficial and subsurficial layers of the 40 m deep borehole mk 6 in koper bay shows practically no enrichment in the former but an increase in the hg and pb contents this would not indicate a rapid increase in eutrophication in the gulf or that the sediments are an important sink for biogenic elements

subsiding shells around shallow cumulus clouds abstract in this study large eddy simulations les are used to gain more knowledge on the shell of subsiding air that is frequently observed around cumulus clouds first a detailed comparison between observational and numerical results is presented to better validate les as a tool for studies of microscale phenomena it is found that horizontal cloud profiles of vertical velocity humidity and temperature are in good agreement with observations they show features similar to the observations including the presence of the shell of descending air around the cloud second the availability of the complete 3d dataset in les has been exploited to examine the role of lateral mixing in the exchange of cloud and environmental air the origin of the subsiding shell is examined by analyzing the individual terms of the vertical momentum equation buoyancy is found to be the driving force for this shell and it is counteracted by the pressure gradient force this shows that evaporative cooling at the cloud edge

numerical simulations of interactions between gravity waves and deep moist convection abstract this study uses a numerical model to simulate deep convection both in the tropics over the ocean and the midlatitudes over land the vertical grid that was used extends into the stratosphere allowing for the simultaneous examination of the convection and the vertically propagating gravity waves that it generates a large number of trajectories are used to evaluate the behavior of tracers in the troposphere and it is found that the tracers can be segregated into different types based upon their position in a diagram of normalized vertical velocity versus displacement conditional sampling is also used to identify updrafts in the troposphere and calculate their contribution to the kinetic energy budget of the troposphere in addition fourier analysis is used to characterize the waves in the stratosphere it was found that the waves simulated in this study have similarities to those observed and simulated by other researchers finally this study examines the wave energy flux as a means to provid

sedimentation rates in relation to sedimentary processes of the yangtze estuary china radioisotope analysis and digital elevation model dem method were combined to examine sedimentation rates and associated sedimentary processes in the yangtze river estuary the major depocenter is validated at the delta front sedimentary facies above the normal wave base nwb where accumulation exceeds erosion this alternated sedimentation does not accommodate pb 210 and cs 137 measurement although sedimentation rates of less than 0 2 5 0 cm yr 1 were recorded in the fine grained silty sediments which were interbedded with coarse grained sandy sediments however historical dem data provide more detailed information on sedimentation in the delta front facies where accumulation is dominant in the sandy shoals 1 73 8 30 cm yr 1 and delta front slope 5 22 cm yr 1 facies the dem data also show that erosion 1 61 7 32 cm yr 1 dominates in the northern estuarine distributaries and accumulation 3 01 4 97 cm yr 1 prevails in the southern ones primarily owing to the superimposed runoff and ebb tidal currents pb 210 and cs 137 measurements reveal sedimentation rate from 2 0 cm yr 1 to 6 3 6 6 cm yr 1 in the delta front slope facies which progressively decreases to 0 8 cm yr 1 in the prodelta facies and is unmeasurable in the delta shelf transition zone dem analysis detects minor erosion in the delta front slope and prodelta facies although accumulation predominates there the present sedimentological database will be useful for estuarine environmental assessment after the three gorges dam is completed in 2009

physical processes and fine grained sediment dynamics coast of surinam south america abstract the prograding holocene mud wedge between the amazon and orinoco rivers in the trade wind belt of northeastern south america provides a modern day example of muds accumulating under moderate wave energy conditions gigantic shore attached mudbanks 10 km 20 km composed partly of thixotropic fluid mud gel front this coast every 30 60 km to form a buffer to wave attack and a temporary storage for fine grained sediments this mesotidal coast tide range 2 0 m with gentle offshore slope 0 0006 allows the exposure twice a day of extensive tidal flat deposits which are backed by mangrove swamps on a well developed chenier plain complex field experiments were conducted in surinam du ing 1975 and 1977 to provide new information on process form relationships in this interesting but unusual muddy environment simultaneous measurements of waves currents tide elevation suspended sediment concentration and variations in mud density show that soft intertidal and subtidal muds are suspended at both tide and wave frequency suspended sediment concentrations typically exceed 1 000 mg l at the surface as incoming solitary like waves partially disperse fluid mud into overlying water on a falling or rising tide redeposition of mud may occur near time of high tide the strong attenuation of shallow water waves by these muds provides conditions that are favorable for further sedimentation high concentrations of suspended fluid mud together with solitary like waves from the northeast throughout the year can lead to extraordinarily high net sediment transport rates in the nearshore zone calculations based on solitary wave theory and on data obtained from this study indicate that 15 65 106 m3 of mud can move along shore each year without involving breaking waves the concept of radiation stress and a nearshore circulation cell or bedload transport farther offshore outside the zone of wave dominance wind driven currents and the guiana current combine to transport muds to the northwest consistent with the observed direction of mudflat migration

estimation of melt pond fraction over high concentration arctic sea ice using amsr e passive microwave data melt pond fraction mpf on sea ice is an important factor for ice albedo feedback throughout the arctic ocean we propose an algorithm to estimate mpf using satellite passive microwave data in this study the brightness temperature tb data obtained from the advanced microwave scanning radiometer earth observing system amsr e were compared to the ship based mpf in the beaufort sea and canadian arctic archipelago the difference between the tb at horizontal and vertical polarizations of 6 9 and 89 0 ghz mp06h 89v respectively depends on the mpf the correlation between mp06h 89v and ship based mpf was higher than that between ship based mpf and two individual channels 6 9 and 89 0 ghz of horizontal and vertical polarizations respectively the mpf determined with the highest resolution channel 89 0 ghz 5 km 5 km provides spatial information with more detail than the 6 9 ghz channel the algorithm estimates the relative fraction of ice covered by water 1 over areas where sea ice concentration is higher than 95 2 during late summer and 3 in areas with low atmospheric humidity the mpf estimated from amsr e data amsr e mpf in early summer was underestimated at lower latitudes and overestimated at higher latitudes compared to the mpf obtained from the moderate resolution image spectrometer modis mpf the differences between amsr e mpf and modis mpf were less than 5 in most the regions and the periods our results suggest that the proposal algorithm serves as a basis for building time series of mpf in regions of consolidated ice pack

a new parameterization for shallow cumulus convection and its application to marine subtropical cloud topped boundary layers part i description and 1d results abstract a new parameterization of shallow cumulus convection is presented the parameterization consists of a mass flux scheme based on a buoyancy sorting entrainment detrainment plume model the mass flux scheme is coupled to a 1 5 order turbulence closure model with an entrainment closure for convective boundary layers model performance is verified using single column model simulations at relatively high vertical resolution of pure trade cumulus convection and a cumulus to stratocumulus transition mixing rates cloud cover and vertical flux profiles as deduced from previously published large eddy simulation studies are well reproduced by the parameterization the model is used to demonstrate that height variations of lateral mixing rates can be successfully captured by a simple implementation of a buoyancy sorting mechanism in the updraft cloud model a companion paper describes the implementation of the scheme in a mesoscale model

isotope fractionation during nitrogen remineralization ammonification implications for nitrogen isotope biogeochemistry abstract the 15 n 14 n isotopic ratio of marine particulate organic matter usually increases as a consequence of preferential 14 n remineralization ammonification during decay in the oxic water column and at the oxic seafloor however a fractionation factor 15 e of sediment ammonification in natural environments has not been determined yet here the 15 e of sedimentary ammonification is calculated in a set of seven sapropel containing sediment cores two subrecent sediment cores and four sediment trap deployments from the eastern mediterranean sea data clearly reveal rayleigh type isotope fractionation and a fractionation factor 15 e between 1 43 and 2 3 hence sediments and probably sinking particulate organic matter as well can be important sources of isotopically depleted reactive nitrogen the knowledge of 15 e further enables to reconstruct paleo export fluxes from sediment cores if original and actual 15 n as well as n accumulation rates are known

organic matter origin and distribution in suspended particulate materials and surficial sediments from the western adriatic sea italy abstract in this study organic carbon oc total nitrogen tn stable carbon isotopic 13 c oc and cuo reaction product compositions were used to identify the sources of organic matter om and to quantify the relative importance of allochthonous and autochthonous contributions to the western adriatic sea italy suspended particulate material 195 samples and surficial sediments 0 1 cm 70 samples from shallow cross shelf transects were collected in february and may 2003 respectively vertical water column profiles were acquired along the same transects data include depth potential temperature salinity density and chlorophyll fluorimetry along the western adriatic shelf in the near shore region the phytoplankton growth was influenced by dynamics of the buoyant plumes from the po and appennine rivers a small amount of very fine terrigenous material remained suspended within the coastal current and was exported southward along the shelf to the slope high variability in the bulk composition was detected in the po prodelta surficial sediments whereas the western adriatic shelf although a larger area exhibited a narrower range of values a significant decoupling was observed between suspended particles in the water column and surficial deposits the organic material collected in the water column was compositionally heterogeneous with contributions from marine phytoplankton riverine estuarine phytoplankton and soil derived om frequent physical reworking of surficial sediments likely leads to the efficient oxidation of marine oc resulting in the observed accumulation and preservation of refractory soil derived oc delivered by the po and appennine rivers

mechanisms of land sea interactions the distribution of metals and sedimentary organic matter in sediments of a river dominated mediterranean karstic estuary this paper examines disposal of metals and the origin characteristics and distribution of sedimentary organic matter som in a mediterranean karstic estuary in the north eastern adriatic this environment offers a real time small model system for studies of geochemical processes in microtidal mediterranean estuaries that are infilling with sediments and classified as river dominated disequilibrium estuaries the results have shown that the longitudinal distribution of heavy metals in sediments follows the sedimentation dynamics and deposition pattern of river borne clay mineral particles the highest concentration of metals was found in the restricted upper part of the estuary characterized by rapid deposition of clay particles and terrestrial sedimentary organic matter and decreases toward the open sea the vertical distribution of metals in sediment cores depends on the prevailing ph and eh conditions significant increases of the concentrations of metals in the uppermost strata are the result of recent anthropogenic inputs the share of the terrestrial component in

transpolar observations of the morphological properties of arctic sea ice save for an area between 8830 0 n and 8930 0 n where polynyas and thin ice were observed surveys of snow depth ice thickness and ice properties were conducted at ice stations thickness observations suggest a general latitudinal trend of increasing ice thickness moving northward with considerable variability from floe to floe and within a single floe average floe thicknesses varied from 1 0 to 2 8 m and the standard deviation of thickness on an individual floe was as large as 1 m ice crystallography showed a large amount of granular ice the average optical equivalent soot content was 4n g cg 1 for new snow 8 ng c g 1 for the surface granular layer of multiyear ice and 18 ng c g 1 for the interior of multiyear ice indicating a tendency of the particulates to concentrate at the surface with melting

the potential of using landsat 7 data for the classification of sea ice surface conditions during summer during spring and summer the surface of the arctic sea ice cover undergoes rapid changes that greatly affect the surface albedo and significantly impact the further decay of the sea ice these changes are primarily the development of a wet snow cover and the development of melt ponds as melt pond diameters generally do not exceed a couple of meters the spatial resolutions of sensors like avhrr and modis are too coarse for their identification landsat 7 on the other hand has a spatial resolution of 30 m 15 m for the pan chromatic band the different wavelengths bands from blue to near infrared offer the potential to distinguish among different surface conditions landsat 7 data for the baffin bay region for june 2000 have been analyzed the analysis shows that different surface conditions such as wet snow and meltponded areas have different signatures in the individual landsat bands consistent with in situ albedo measurements melt ponds show up as blueish whereas dry and wet ice have a white to gray appearance in the landsat true color image these spectral differences enable the distinction of melt ponds the melt pond fraction for the scene studied in this paper was 37