a coal depositional model for the durham coal measures of ne england the upper carboniferous westphalian coal measures of the durham coalfield were deposited on a broad flat deltaic plain in early westphalian a times a lower delta plain setting prevailed evolving through southward deltaic progradation into an upper delta plain by mid westphalian a detailed facies analysis of large opencast exposures supported by extensive subsurface data has shown that a hierarchy of depositional controls operated across the durham area during westphalian times i on the large scale depositional geometry was controlled by patterns of major delta progradation and switching ii on the medium scale by a combination of structurally and compactionally induced subsidence and iii on the small scale by local sedimentary processes and subsidence patterns these observations form the basis of a coal depositional model for the durham coal measures which predicts that the thickest coals are to be found in upper delta plain domains controlled by compactional subsidence and not underlain by substantial channel sandstones this model may also be applicable to other coalfields of northern england and to ancient delta plain sequences elsewhere in the world

effects of wind stress and wind stress curl variability on coastal upwelling abstract aircraft measurements during the winter 1989 shelf mixed layer experiment smile and summer 1982 coastal ocean dynamics experiment code were used to characterize the spatial variation of the low level wind and wind stress over the northern california shelf the curl of the wind stress was calculated from directly measured turbulent stress components the accuracy of the computed curl was estimated to be adequate to map the spatial structure wintertime measurements showed a concentration of large positive curl over 1 pa 100 km 1 west of point arena regardless of wind direction due to the effects of the coastal topography on the wind fields results from summertime measurements showed a similar local maximum of positive curl west of point arena larger curl values over 3 5 pa 100 km 1 however were observed across a hydraulic jump propagating from stewarts point for highly supercritical marine boundary layer flow a two layer vertically integrated numerical model of coastal upwellin

investigation of multiple reflections and wave conversion by means of a vertical wave test vertical seismic profiling in southern mississippi a vertical wave test employing the vertical seismic profiling vsp technique in southern mississippi confirmed suspicions that apparent multiple reflections might include converted waves as well as multiply reflected compressional waves both compressional p and shear s waves generated near the source were observed to travel to great depths and p to s conversions were apparent in deep zones as well as shallow p wave reflections were observed in agreement with predictions from synthetic records based on the sonic log up traveling p waves were reflected a short distance below the surface at the base of the low velocity layer and were followed as down traveling p waves to 200 ft depth by means of a vertical spread below 2000 ft and following the first p wave train the predominate energy appeared to be down traveling p waves which could not be traced back to the reflection of up traveling p waves the continuity of wavelets indicated instead that the strong down traveling s waves generated near th

direct observations of velocity and transport in the passages between the intra americas sea and the atlantic ocean 1984 1996 shipboard acoustic doppler current profiler observations of the velocity in the upper 200 m of the water column collected during 1984 1996 using the national oceanic and atmospheric administration r v malcolm baldrige are used to examine the velocity structure and transport in the passages between the atlantic ocean and the intra americas sea ias data were collected during 23 cruises along the following sections across the straits of florida in the northwest providence channel nwpc across the northern passages into the caribbean sea windward mona and anegada across the eastern caribbean along 63 30 w thereby forming a closed quadrangle and in the grenada passage the florida current the eastern caribbean and the grenada passage share a similar mean velocity structure characterized by high velocity surface intensified flows with strong vertical and horizontal shears the northern caribbean passages nwpc windward mona and anegada share a different common mean velocity structure with subsurface velocity maxima directed into the ias and surface intensified counterflows along one side of each passage on average there is a transport balance in the upper 200 m between waters entering and exiting the ias with the 16 5 2 4 sv 1 sv 106 m3 s transport of the florida current at 27 n comprised of 0 4 0 8 sv from the nwpc 2 2 1 5 sv from the windward passage 2 8 2 1 and 2 4 2 8 sv from the mona and anegada passages respectively and 9 5 4 7 sv across the eastern caribbean for a total of 17 3 sv the four passages north of 17 n from nwpc to anegada passage have a combined transport of 7 8 sv nearly half of the transport of the florida current in the upper 200 m of the 9 5 sv flowing through the eastern caribbean between 11 n and 17 n 4 9 2 6 sv or more than half come from the grenada passage this is significant to the subject of cross equatorial exchange of mass heat and salt as the grenada passage is where the highest transport of waters originating in the southern hemisphere is thought to enter the caribbean

surface currents in the caribbean sea as deduced from lagrangian observations the results of a satellite tracked drifting buoy experiment conducted in the caribbean sea from october 1975 through june 1976 are presented the buoy trajectories suggest that the aves rise beata ridge and nicaraguan rise are regions where considerable mesoscale variability occurs in the surface flow the variability is in the form of current deflections small diameter eddies ranging in size from 20 to 100 km large amplitude meanders with amplitudes greater than 150 km and large diameter eddies with diameters greater than 200 km which form on and near these rises and ridges in the central caribbean where the topographic relief is not as dramatic the flow is predominantly zonal intensifications in the surface flow occur off the coast of colombia south of the nicaraguan rise and south of the yucatan strait

lagrangian flow observations of the amazon river discharge into the north atlantic nine satellite tracked drifters with near surface drogues were launched in or near the mouth of the amazon river on the north brazil shelf during 1989 1991 at four different stages of river discharge the drifters initially moved along shelf toward the northwest over the north brazil shelf with mean speeds varying from 41 to 128 cm s and a maximum along shelf velocity of 197 cm s many drifters experienced strong acceleration near 2 n between the 5 m and 20 m isobaths caused in part by the sharp reduction in cross shelf cross sectional area near the shore perpendicular cabo norte shoal the drifter trajectories showed strong cross shelf tidal variability in the flow field near the amazon river mouth and the largest low frequency along shelf variability was located over the open shelf just north of cabo norte good visual correlation between drifter along shelf velocity and along shelf wind stress supports the dynamical model of lentz this issue that subtidal fluctuations in near surface along shelf currents in the amazon river plume are strongly wind driven drifters left the north brazil shelf after about 5 to 30 days three drifters moved northwestward parallel to the northeast coast of south america crossed the shelf break near 8 n and moved into deeper north atlantic water where they began looping in anticyclonic eddies often called retroflection eddies or loopers with periods of approximately 11 days as they moved northwestward to the caribbean sea four drifters initially moved along shelf toward the northwest and then offshore between 3 n and 7 n where they followed the retroflection of the north brazil current only one drifter entered the zonal current system that characterizes the equatorial atlantic circulation

planetary and synoptic scale signatures associated with central american cold surges abstract motivated by outstanding issues from a previous case study of a midlatitude cold surge that affected mexico and central america the climatology of central american cold surges is examined in this paper an independently derived listing of 177 cold surge events is employed for which the following properties are tabulated onset date duration time between cold surge events latitude of maximum equatorward penetration min and 48 h maximum surface temperature change at merida mexico t these data show that 75 of the cold surges have durations of 2 6 days the same timescale as mobile disturbances in the westerlies also there does not appear to be any relationship between t and the duration of the event although cold surges that penetrate to low latitudes min 7 10 n have a weak tendency to persist longer than those that do not penetrate to low latitudes min 15 20 n in addition the reding data indicate that the cold surges tend to reach their most equatorward extent where

sequence stratigraphy of paralic coal bearing strata an overview abstract sequence stratigraphy arose in the late 1980s to fundamentally change the science of stratigraphy former practice of labeling formations and erecting stratigraphic columns gave place to a dynamic genetic stratigraphic analysis where the main concern is about understanding the history of sedimentation and to establish models able to predict facies born and mainly applied to an environment of petroleum prospecting and exploration sequence stratigraphy has gained entrance to other branches of sedimentary geology the present paper gives a short introduction to sequence stratigraphic concepts and shows an overview of its application on coal bearing strata two case studies one from the early permian coals of the parana basin brazil and one from the lower cretaceous coals of the western canada sedimentary basin illustrate the concepts

hydrocarbon prospectivity of the cooper basin australia the pennsylvanian middle triassic cooper basin is australia s premier conventional onshore hydrocarbon producing province the basin also hosts a range of unconventional gas play types including basin centered gas and tight gas accumulations deep dry coal gas associated with the patchawarra and toolachee formations and the murteree and roseneath shale gas plays this study used petroleum systems analysis to investigate the maturity and generation potential of 10 permian source rocks in the cooper basin a deterministic petroleum systems model was used to quantify the volume of expelled and retained hydrocarbons estimated at 1272 billion boe 512 billion bbl and 760 billion boe and 977 billion boe 362 billion bbl and 615 billion boe respectively monte carlo simulations were used to quantify the uncertainty in volumes generated and to demonstrate the sensitivity of these results to variations in source rock characteristics the large total generation potential of the cooper basin and the broad distribution of the permian source kitchen highlight the basin s significance as a world class hydrocarbon province the large disparity between the calculated volume of hydrocarbons generated and the volume so far found in reservoirs indicates the potential for large volumes to remain within the basin despite significant losses from leakage and water washing the hydrocarbons expelled have provided abundant charge to both conventional accumulations and to the tight and basin centered gas plays and the broad spatial distribution of hydrocarbons remaining within the source rocks especially those within the toolachee and patchawarra formations suggests the potential for widespread shale and deep dry coal plays

statistical analysis of the surface circulation in the california current system using satellite tracked drifters abstract a kinematic description of the surface circulation in the southern california current system is presented using the statistics of the 7 11 month long trajectories of 29 satellite tracked mixed layer drifters the drifters were released north of 30 n and traveled southward at an average speed of 3 4 cm s 1 along baja california through an inhomogeneous field of mesoscale eddies of 15 cm s 1 rms variability lagrangian and eulerian statistics of the variations about this mean southward drift are computed the drifter ensemble mean lagrangian decorrelation time scale is 4 5 days and the lagrangian decorrelation space scale is 40 50 km the computation of dispersion of single particles about the mean drift shows that the theory of diffusion by homogeneous random motion taylor s theory describes these dispersive motions well ensemble mean diffusivities of about 4 107 cm2 s 1 are found on a 200 200 km2 spatial average single partial diffusivities are found to be proportional to the kinetic ene

application of a high resolution seismic investigation in a greek coal mine high resolution seismic methods were applied to map the detailed structure and thickness of the domeniko coal basin central greece and to search for lateral discontinuities such as pinch outs and faults extensive tests were performed to optimize recording parameters and equipment reflection events which can be attributed to coal layers can be interpreted from depths of approximately 30 to 150 m on cdp stacked and inverted sections several low throw faults have been interpreted from the sections results obtained from the high resolution seismic reflection survey combined with drillhole information clearly revealed the 3 d model of the coal field using geostatistical methods the results of the high resolution reflection seismic survey were combined with the information from the borehole program to clearly reveal the 3 d model of the basin

hydrological and sedimentary controls leading to arsenic contamination of groundwater in the hanoi area vietnam the impact of iron arsenic ratios peat river bank deposits and excessive groundwater abstraction groundwater contamination by arsenic in vietnam poses a serious health threat to millions of people in the larger hanoi area elevated arsenic levels are present in both the holocene and pleistocene aquifers family based tubewells predominantly tap the holocene aquifer while the hanoi water works extract more than 600 000 m3 day of groundwater from the pleistocene aquifer detailed groundwater and sediment investigations were conducted at three locations exhibiting distinct geochemical conditions i e i high levels of dissolved arsenic av 121 g l at the river bank ii low levels of dissolved arsenic av 21 g l at the river bank and iii medium levels of dissolved arsenic 60 g l in an area of buried peat and excessive groundwater abstraction seasonal fluctuations in water chemistry were studied over a time span of 14 months sediment bound arsenic 1 3 22 g g is in a natural range arsenic correlates with iron r2 0 8 with variation related to grain size sediment leaching experiments showed that arsenic can readily be mobilized at each of the three locations low levels of arsenic in groundwater 10 g l generally exhibit manganese reducing conditions whereas elevated levels are caused by reductive dissolution under iron and sulphate reducing conditions average arsenic concentrations in groundwater are twofold higher at the river bank than in the peat area the lower levels of arsenic contamination in the peat area are likely controlled by the high abundance of iron present in both the aqueous and sediment phases with median molar fe as ratios of 350 in water and 8700 in the sediments of the peat area reduced iron possibly forms new mineral phases that resorb or sequester previously released arsenic to the sediment despite similar redox conditions resorption is much less significant at the river bank fe as aq 68 fe as s 4700 and hence arsenic concentrations in groundwater reach considerably higher levels drawdown of holocene water to the pleistocene aquifer in the peat area caused by the pumping for the hanoi water works clearly promotes reducing conditions in pleistocene groundwater this demonstrates that excessive abstraction of water from deep wells i e wells tapping water below the arsenic burdened depth can cause a downward shift of iron reducing conditions and concurrently mobilize arsenic along the way vertical migration of reduced groundwater may also impact aquifers under natural hydrological conditions seepage of doc enriched groundwater derived from degradation of organic matter in the clayey sediments at the river bank was observed to enhance and maintain iron reducing conditions in the aquifer where organic matter is scarce once the aquifer becomes reduced arsenic is released from the aquifer solid hosts but additionally derives from the arsenic enriched groundwater seeping from the clay into the aquifer this behaviour is an important mechanism for arsenic contamination in aquifers that might not necessarily contain enough organic matter in their sediments to induce reducing conditions independently

impact of irrigation with as rich groundwater on soil and crops a geochemical case study in west bengal delta plain india abstract the distribution of as was explored in soils and crops in order to investigate the influence of irrigation with as rich groundwater on the soil plant system and to determine its impact on the environment and human health the study was carried out in an intensively cultivated agricultural area of the bengal delta plain west bengal india soils plants and irrigation water from adjacent rice and wheat fields were analysed for as and other elements irrigation water has concentrations of up to 780 g l 1 as in the study area rice and wheat grains are not contaminated by as about 0 3 and 0 7 mg kg 1 respectively but concentrations in rice roots were found to be 169 178 mg kg 1 as which is more than 20 times higher than value of 7 7 mg kg 1 measured at the uncontaminated reference site this high content is due to an fe rich plaque which coats the rice roots a significant increase of as concentration was registered also in the stems of the rice plants irrigated with as rich groundwater 6 55 7 06 relative to 0 36 mg kg 1 as in the reference plant arsenic concentration in the uppermost soil layers of the rice paddy field 38 mg kg 1 was found to be roughly twice as high as in the soil of the less intensively watered wheat field 18 mg kg 1 and more than 5 times higher than in the soil of a rice paddy irrigated with uncontaminated water 7 mg kg 1 in both soil sections as contents decreased downwards to 11 mg kg 1 at 100 110 cm depth approaching the background value of 5 10 mg kg 1 measured in an unaffected reference area sequential extraction experiments show that most of the mobile as in soils is bound to fe oxides though no tight correlation was found between fe and as in the bulk soil samples these experiments coupled with synchrotron radiation xrf analysis of single soil particles from the rice paddy also indicates that additional to the mobile fraction a substantial part of as is immobilized in chiefly fe bearing silicates in rice soil some as was also found in the sulphide bearing phase of the extraction

isotope and minor element geochemistry of high arsenic groundwater from hangjinhouqi the hetao plain inner mongolia abstract high as groundwater is widely distributed in the northwestern hetao plain an arid region with slow groundwater flow arsenic concentration in groundwater ranges from 1 to 1000 g l most water samples have elevated salinities with cl and or hco 3 as the dominant anions and na as the dominant cation high concentrations of as in shallow aquifers are associated with strongly reducing conditions as evidenced by high concentrations of dissolved organic c doc nh 4 dissolved sulfide arsenite and dissolved ch 4 and relatively low concentrations of no 3 and so 4 2 results of the hydrochemical and h and o isotope geochemical studies indicate that evapotranspiration is an important process controlling the enrichment of na and cl as well as trace elements such as as b f and br in groundwater in na hco 3 dominated groundwaters as b and f were enriched decades of irrigation using yellow river water has resulted in elevation of the groundwater level which has accelerated salt accumulation in shallow groundwater and surface soil in addition irrigation is responsible for the release of some components from aquifer materials and mixing with saline groundwaters as indicated by minor element and isotope geochemical data used to trace groundwater flow paths sr isotope composition also indicates that bedrock weathering is one of the primary sources of as in groundwater in the study area

review of arsenic geochemical characteristics and its significance on arsenic pollution studies in karst groundwater southwest china abstract as a metalloid element arsenic as is widely distributed in the natural environment its ingestion can cause cancer deformities and mutations therefore it has become an important environmental problem in recent years there are large amounts of arsenic ore and coal with high arsenic content in southwest china a karst area there arsenic occurs in wastewater from mines contaminate soil vegetation and surface water karst underground aquifers are also contaminated through pipes cracks scuttles and sinkholes leading to a more serious arsenic pollution problem than in non karst areas due to the unique karst hydrogeological conditions to prevent and curb karst underground water contamination and guarantee water resource security and public health a review on the arsenic contamination in the karst area is necessary this paper discusses the progress of geochemical studies on arsenic through an analysis of the hydrogeology of karst areas this paper proposes that studies on arsenic pollution in karst regions should be combined with the spatial distribution and redox characteristics of groundwater more attention should be paid to chemical compositions of water soil and rocks as well as adsorption desorption processes between water and sediment when conducting arsenic geochemical research in karst groundwater

can thin coals be resolved in seismic data an example of the challenges for carboniferous visean to westphalian source rock definition across the elbow spit platform netherlands and the mid north sea high uk through well synthetic modelling

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

circulation of the caribbean sea a well resolved inverse problem the caribbean sea is selected as a region where the large scale circulation is well determined by historical hydrographic measurements through application of the inverse method a simple example is used to illustrate the technique and to demonstrate how some physically relevant quantities may be well determined in the formally underdetermined inverse problem the geostrophic flow field in the caribbean is found by imposing mass and salt conservation constraints in seven layers separated by surfaces of constant potential density an unsmoothed solution is displayed that has weak dependence on an initial choice of reference level in addition a unique smoothed solution is shown above sigma sub theta 27 4 the total flow leaving the western caribbean is estimated to be 29 x 10 sup 6 m sup 3 s sup 1 in agreement with direct measurements this flow is made up of 22 x 10 sup 6 m sup 3 s sup 1 entering the caribbean from the east and flowing across the southern half of the basin as the caribbean current and 7 x 10 sup 6 m sup 3 s sup 1 in agreement with direct measurements this flow is made up of 22 x 10 sup 6 m sup 3 s sup 1 entering the caribbean from the east and flowingmore across the southern half of the basin as the caribbean current and 7 x 10 sup 7 m sup 3 s sup 1 entering from the north through windward passage both of these currents show small scale variability that diminishes with distance from the respective passages the deep flow has no net transport as required by the shallow exit but a well organized clockwise recirculation is found in the deep eastern caribbean less

some examples of detection of oceanic mesoscale eddies by the seasat synthetic aperture radar this note presents images of three dynamically different regions in the ocean to demonstrate the variety of mesoscale variabilities detected by the seasat synthetic aperture radar sar south of the grand banks of newfoundland a cold eddy is observed to form as the result of the southward intrusion of labrador sea water perhaps having led to the birth of a gulf stream extension ring off the northern coast of california features resulting from the offshore intrusions of cold upwelling water are observed two topographically generated eddies are detected near misteriosa bank on the cayman ridge in the northwestern caribbean comparisons are made with concurrent noaa 5 infrared images whenever the eddies have thermal signatures

sequence stratigraphy of coastal alluvial plain westphalian b coal measures in northumberland and the southern north sea abstract westphalian b coastal alluvial plain coal measures of northumberland and the southern north sea are susceptible to stratigraphic base level fluctuations of various magnitudes which create a hierarchy of flooding surfaces 1 high magnitude third order maximum flooding surfaces corresponding to the anthracoceratites vanderbeckei and anthracoceras aegiranum marine bands defining the top and bottom of the succession when vast areas of the westphalian foreland basin were flooded by marine incursions 2 high frequency fluctuations promoting small scale fourth order flooding of the entire or large areas 100 s km 2 of the alluvial plain resulting in deposition of non marine bivalve beds or marine bands depending on their position on the third order base level curve and 3 small scale localised base level rises due to differential compaction and autocyclic switching of minor crevasse splays and distributary channels a regionally extensive third order tectonically induced sequence boundary is also recognised in the southern north sea slightly above the maximum stand in stratigraphic base level recorded by the vanderbeckei marine band this sequence boundary which represents the lowest point on the background eustatic base level curve between the two maximum flooding surfaces is overlain by the multilateral multistorey caister sandstone the lack of significant erosional relief beneath this channel sandstone suggests that accommodation space at this time was being created at a very low rate the succession above the caister sandstone sequence boundary up to the aegiranum marine band maximum flooding surface records an increasing rate of stratigraphic base level rise this equates to a third order transgressive systems tract or sequence set comprising a number of fourth order sequences which change upwards in response to the background low frequency rise the increasing rate of base level rise and increased accommodation space is accompanied by a change in fluvial style to more isolated channels enclosed within floodplain deposits

the surface circulation of the caribbean sea and the gulf of mexico as inferred from satellite altimetry the surface circulation of the caribbean sea and gulf of mexico is studied using 13 years of satellite altimetry data variability in the caribbean sea is evident over several time scales at the annual scale sea surface height ssh varies mainly by a seasonal steric effect interannually a longer cycle affects the ssh slope across the current and hence the intensity of the caribbean current this cycle is found to be related to changes in the wind intensity the wind stress curl and el nino southern oscillation at shorter time scales eddies and meanders are observed in the caribbean current and their propagation speed is explained by baroclinic instabilities under the combined effect of vertical shear and the b effect then the loop current lc is considered focusing on the anticyclonic eddies shed by it and the intrusion of the lc into the gulf of mexico through time twelve of the 21 anticyclonic eddies observed to detach from the lc are shed from july to september suggesting a seasonality in the timing of these events also a relation is found between the intrusion of the lc into the gulf of mexico and the size of the eddies shed from it larger intrusions trigger smaller eddies a series of extreme lc intrusions into the gulf of mexico when the lc is observed as far as 928w are described the analyses herein suggest that the frequency of such events has increased in recent years with only one event occurring in 1993 versus three from 2002 to 2006 transport through the straits of florida appears to decrease during these extreme intrusions

eddies in the north brazil current retroflection region observed by geosat altimetry mesoscale fluctuations in the western tropical atlantic are analyzed in geosat altimetry sea surface height ssh and geostrophic velocity anomalies to investigate the role of eddies in the north brazil current nbc retroflection zone the detachment of anticyclonic eddies from the nbc retroflection is observed during november through january when the nbc retroflection into the north equatorial countercurrent necc weakens and finally breaks down these eddies are traced over more than 2 months between 50 and 60 w on their way toward the caribbean at average speeds of 15 cm s 1 in one case an apparent merger of two anticyclonic eddies occurs one detached from the retroflection zone and one detached from the necc cyclonic eddies are also observed but are generally less persistent mesoscale ssh variance just west of the retroflection increases by a factor of 2 from early summer to winter mainly because of the anticyclonic eddies interhemispheric water mass transfer associated with the eddy flux out of the nbc retroflection may amount to an average transport of 3 sv

on the surface currents of the caribbean sea 1 velocity observations from near surface drifters made between 1996 and 2001 were used to construct surface circulation maps of the caribbean sea in the venezuela basin the strongest westward currents 0 3 ms 1 are found south of 14 n and at 17 n two jets occur over the deep gaps of the jamaica ridge and move northwestward across the cayman basin the two jets feed a current that impinges on yucatan slows down while turning north and accelerates again to become the yucatan current a cyclonic gyre occurs in the southern colombia basin with mean currents along the south coast in excess of 0 7 m s 1 to the east the gyre is highly variable eddy motions dominate most of the eastern caribbean as well as the eastern yucatan basin where the average surface circulation is not well defined

seismic facies analysis of westphalian sequences of the southern north sea abstract differing seismic facies are observed from within the westphalian sequences of the southern north sea a review of published synthetic seismograms and seismic data from known coal bearing basins establishes seismic facies types and their relationships similar reflection character is recognized from westphalian sequences in the southern north sea and lithologies confirmed by borehole information probable sand silt or clastic prone upper coal measures westphalian c d stages and coal prone lower and middle coal measures westphalian a b and part c stages can be defined and mapped providing information on the regional distribution of source and reservoir rocks and stratigraphic plays it is suggested that sand prone channel complexes or clastic dominated areas within the mainly a b stages can be recognized and mapped providing information on migration pathways and stratigraphic plays

north atlantic surface circulation during the 1990 s observed with satellite tracked drifters a new compilation of lagrangian velocity observations describes the state of the north atlantic surface circulation during the 1990s gridded fields of velocity and eddy kinetic energy eke are constructed from trajectories of more than 1500 15 m drogued satellite tracked surface drifters in service between january 1990 and december 1999 this time period overlaps a coordinated field study of circulation and variability in the north atlantic completed between 1996 2000 as part of the world ocean circulation experiment we describe the construction of a self consistent drifter climatology present decadal mean quasi eulerian velocity and eke fields computed on a 1 grid and compare these results with contemporary satellite measurements detailed discussion of the inferred surface circulation is focused on three regions 1 the gulf stream and north atlantic current 2 the labrador sea and subpolar gyre and 3 the caribbean sea the swiftest drifter motions were found in the equatorial region and along the tropical subtropical and subpolar western boundaries the maximum instantaneous speed determined from a single quality controlled and filtered drifter observation was 273 cm s 1 in the gulf stream southeast of cape cod the highest eke value in the north atlantic 2790 cm2 s 2 was found in the gulf stream just downstream of the new england seamounts over most of the atlantic basin drifter derived eke values were found to be o 100 cm2 s 2 higher than corresponding values derived from satellite altimetry in the labrador sea a region of sharply elevated eke appears to be geographically related to the localized ejection of drifters and by extension mass and kinetic energy from the energetic west greenland current between 60 and 62 n when compared to drifter measurements made in the late 1970s our results suggest but do not statistically confirm an enhancement and slight northward shift of the zonal gulf stream extension such a shift is consistent in sign with expectations based on observed interdecadal variations in wind stress and subtropical gyre potential energy associated with the north atlantic oscillation

arsenic associations in sediments from shallow aquifers of northwestern hetao basin inner mongolia understanding the mechanism of arsenic mobilization from sediments to groundwater is important for water quality management in areas of endemic arsenic poisoning such as the hetao basin in inner mongolia northern china aquifer geochemistry was characterized at three field sites sh hf tys in hangjinhouqi county of northwestern hetao basin the results of bulk geochemistry analysis of sediment samples indicated that total as concentrations have a range of 6 8 58 5 mg kg with a median of 14 4 mg kg the highest as concentrations were found at 15 25 m depth in the meanwhile the range of as concentration in the sediments from background borehole is 3 21 8 mg kg with a median value of 9 mg kg the as sediments concentrations with depth from the sh borehole were correlated with the contents of fe sb b v total c and total s generally the abundance of elements varied with grain size with higher concentrations in finer fractions of the sediments distinct lithology profile and different geochemical characteristics of aquifer sediments indicate the sediments are associated with different sources and diverse sedimentary environments up to one third of arsenic in the sediments could be extracted by ammonium oxalate suggesting that fe oxyhydroxides may be the major sink of as in the aquifer sequential extraction results indicate that arsenic occurs as strongly adsorbed on and or co precipitated with amorphous fe oxyhydroxides in sediments accounting for 35 and 20 respectively of the total contents of arsenic the release of as into groundwater may occur by desorption from the mineral surface driven by reductive dissolution of the fe oxide minerals furthermore small proportions of as associated with iron sulfides occur in the reductive sediments

effects of central american mountains on the eastern pacific winter itcz and moisture transport the intertropical convergence zone itcz is displaced to the south edge of the eastern pacific warm pool in boreal winter instead of being collocated a high resolution regional climate model is used to investigate the mechanism for this displaced itcz under the observed sea surface temperature sst and lateral boundary forcing the model reproduces the salient features of eastern pacific climate in winter including the southward displaced itcz and gap wind jets off the central american coast as the northeast trades impinge on the mountains of central america subsidence prevails off the pacific coast pushing the itcz southward cold sst patches induced by three gap wind jets have additional effects of keeping the itcz away from the coast in an experiment in which both the central american mountains and their effect on sst are removed the itcz shifts considerably northward to cover much of the eastern pacific warm pool the central american mountains are considered important to freshwater transport from the atlantic to the pacific ocean which in turn plays a key role in global ocean thermohaline circulation the results of this study show that this transport across central america is not very sensitive to the fine structure of the orography because the increased flow in the mountain gaps in a detailed topography run tends to be compensated for by broader flow in a smoothed topography run implications for global climate modeling are discussed

arsenic associations in sediments from the loess aquifer of la pampa argentina groundwater from the quaternary loess aquifer of la pampa central argentina has significant problems with high concentrations of as up to 5300 g l 1 as well as other potentially toxic trace elements such as f b mo u se and v total as concentrations in 45 loess samples collected from the aquifer have a range of 3 18 mg kg 1 with a mean of 8 mg kg 1 these values are comparable to world average sediment as concentrations five samples of rhyolitic ash from the area have as concentrations of 7 12 mg kg 1 chemical analysis included loess sediments and extracted porewaters from two specially cored boreholes results reveal a large range of porewater as concentrations being generally higher in the horizons with highest sediment as concentrations the displaced porewaters have as concentrations ranging up to 7500 g l 1 as well as exceptionally high concentrations of some other oxyanion species including v up to 12 mg l 1 the highest concentrations are found in a borehole located in a topographic depression which is a zone of likely groundwater discharge and enhanced residence time comparison of sediment and porewater data does not reveal unequivocally the sources of the as but selective extract data acid ammonium oxalate and hydroxylamine hydrochloride suggest that much of the as and v is associated with fe oxides primary oxides such as magnetite and ilmenite may be partial sources but given the weathered nature of many of the sediments secondary oxide minerals are probably more important extract compositions also suggest that mn oxide may be an as source the groundwaters of the region are oxidising with dissolved o2 no3 and so4 normally present and as v usually the dominant dissolved as species under such conditions the solubility of fe and mn oxides is low and as mobilisation is strongly controlled by sorption desorption reactions desorption may be facilitated by the relatively high ph conditions of the groundwaters in the region 7 0 8 8 and high concentrations of potential competitors e g v p hco3 phreeqc modelling suggests that the presence of v at the concentrations observed in the pampean porewaters can suppress the sorption of as to hydrous fe iii oxide hfo by up to an order of magnitude bicarbonate had a comparatively small competitive effect oxalate extract concentrations have been used to provide an upper estimate of the amount of labile as in the sediments a near linear correlation between oxalate extractable and porewater as in one of the cored boreholes investigated has been used to estimate an approximate kd value for the sediments of 0 94 l kg 1 this low value indicates that the sediments have an unusually low affinity for as

carboniferous petroleum systems around the mid north sea high uk the existence of an extensive prospective visean namurian carboniferous petroleum system in and around the hitherto under explored mid north sea high is documented evidence is drawn from integrated analysis of over 50 000 line kilometres of seismic data and well data together with regional source rock screening reservoir analysis and basin modelling visean namurian marine and non marine mudstones and coal source rocks are interbedded within fluvial and marine reservoir sandstones within a stacked succession up to 5 km thick source rocks are dominantly gas prone with oil prone intervals and have reached oil to gas maturity levels dependent on location burial thermal history modelling indicates a kitchen area on the southern margin of the mid north sea high with northwest and northeastwards migration of gas and oil during mesozoic and cenozoic times a variety of structural and stratigraphic traps are possible including intraformational carboniferous traps with a regional seal at permian zechstein level synthesis of many previously unpublished datasets demonstrates the visean namurian play south of the mid north sea high as part of an extensive petroleum system from the east irish sea across onshore to offshore uk and into the netherlands sector of the north sea the purpose of this synthesis is to highlight future exploration opportunities beneath and northwards of the productive westphalian southern north sea gas basin and to begin to de risk the petroleum systems that are exemplified by the lower carboniferous breagh field in a frontier area of the mature north sea province

tropical instability vortices in the atlantic ocean 1 this paper examines the physical characteristics and dynamics of atlantic tropical instability vortices based on observational data from 1997 to 2000 and a high resolution numerical model simulation most prominent during boreal summer the vortices are characterized by 400 km spatial scales westward translation at 0 40 cm s 1 anticyclonic circumferential velocities of 30 110 cm s 1 and sstanomalies that decrease from 2 ci n midbasin to 0 5 c or less near the western boundary in contrast the sea level anomalies grow as the vortices progress westward reaching maximum amplitudes of 14 cm near 40 w the large circumferential velocities leading to relative vorticities of 4 10 6 s 1 and rossby numbers of 0 5 indicate that centrifugal effects may play an important role in the vortices vorticity balance we address the vortices vertical structure and vorticity dynamics by examination of a high resolution numerical model there is a reasonably good agreement between the model and observations simulated vortices are confined mostly to the mixed layer which increases westward in depth from 30 to 100 m near the western boundary in the eastern basin potential vorticity within the vortices is not conserved but decreases because of wind stress forcing in contrast in the western basin decreases in potential vorticity are due mostly to the vortices acquisition of southern hemisphere water we estimate an annualized cross equatorial transport of up to 1 2 sv associated with the vortices which is eventually contributed to the north brazil current system index terms 4231 oceanography general equatorial oceanography 4520 oceanography physical eddies and mesoscale processes 4528 oceanography physical fronts and jets keywords tropics instability atlantic

chemical evolution in the high arsenic groundwater of the huhhot basin inner mongolia pr china and its difference from the western bengal basin india elevated as concentrations in groundwater of the huhhot basin hb inner mongolia china and the western bengal basin wbb india have been known for decades however few studies have been performed to comprehend the processes controlling overall groundwater chemistry in the hb in this study the controls on solute chemistry in the hb have been interpreted and compared with the well studied wbb which has a very different climate physiography lithology and aquifer characteristics than the hb in general there are marked differences in solute chemistry between hb and wbb groundwaters stable isotopic signatures indicate meteoric recharge in the hb in a colder climate distant from the source of moisture in comparison to the warm humid wbb the major ion composition of the moderately reducing hb groundwater is dominated by a mixed ion ca na hco3 cl hydrochemical facies with an evolutionary trend along the regional hydraulic gradient molar ratios and thermodynamic calculations show that hb groundwater has not been affected by cation exchange but is dominated by weathering of feldspars allitization and equilibrium with gibbsite and anorthite mineral weathering and mobilization of as could occur as recharging water flows through fractured argillaceous metamorphic or volcanic rocks in the adjoining mountain front areas and deposits solutes near the center of the basin in contrast wbb groundwater is ca hco3 dominated indicative of calcite weathering with some cation exchange and silicate weathering monosiallitization

sedimentogenesis and hydrobiogeochemistry of high arsenic late pleistocene holocene aquifer systems geogenic enrichment of arsenic as in groundwater has been a topic of worldwide concern over the past several decades due to the severe health threat to an estimated over one hundred million people despite the genetic diversity and the spatial variability of as concentrations the most common geogenic as enriched groundwater occurs in flat low lying river floodplains and fluvial lacustrine plains within river systems draining the himalaya tectonic movement sedimentological processes and palaeoclimatic optima after the last glacial maximum have created favorable conditions for the formation of high as aquifer systems mainly within the late pleistocene holocene deposits the co deposition of as bearing fe oxides and reactive organic matter within sediments of deltas floodplains or fluvial lacustrine plains forms the premise for as release under reducing geochemical environments however depending on the reactivity of organic matter and as bearing fe oxides as well as the availability of aqueous sulfate geochemical mechanisms controlling as enrichment in the groundwater differ between the coastal floodplains of south and southeast asia and the fluvial lacustrine plains of north and central china the indigenous geomicrobes thriving to adapt to specific aquifer environments may mediate fe s as biogeochemical cycling responsible for as speciation transformation dissolution desorption and hence mobilization hydrologic processes regulated by the local and regional groundwater flow regimes control as transport as well as its spatial distribution special attention must be paid to anthropogenic perturbation from intensive groundwater pumping and land use changes that affect the aquifer hydrological conditions and the biogeochemical processes thus altering groundwater as levels to decipher the patterns of as variation within the aquifers an integrated approach characterizing the major sedimentological hydrobiogeochemical and anthropogenic processes influencing as release and transport needs to be applied to ensure sustainable water supply for domestic and agricultural needs

can hydrocarbon source rocks be identified on seismic data hydrocarbon source rocks contain signifi cant volumes of organic matter are capable of expelling petroleum when heated and have produced most of the world s known oil volumes recently source rocks have also become recognized as unconventional economic reservoirs here we present a new way of identifying characterizing and mapping spatial distributions and variations of thick source rocks 20 m that is based on seismic data only this has a signifi cant impact on the prospect risk assessment of petroleum plays rock property studies of organic rich claystones show that the acoustic impedance ai which is the product of compressional velocity and density decreases nonlinearly with increasing total organic carbon toc percent claystones mixed with low density organic matter toc 3 4 have signifi cant lower ai and higher intrinsic anisotropy than otherwise similar nonorganic claystones this gives the top and base source rock refl ections characteristic negative and positive high amplitudes respectively which dim with increasing refl ection angle in addition the toc profi le which is a smoothed toc percent curve infl uences the top and base amplitude responses an upward increasing toc profi le has the highest amplitude at the top while the opposite asymmetry is observed for downward increasing toc profi les by using seismic data we therefore can map lateral distribution thickness variation in toc profi les and with local well calibration convert ai data to toc percent this approach to mapping source rocks may change the way petroleum systems are evaluated

mobilization of arsenic and iron from red river floodplain sediments vietnam abstract sediments from the red river and from an adjacent floodplain aquifer were investigated with respect to the speciation of fe and as in the solid phase to trace the diagenetic changes in the river sediment upon burial into young aquifers and the related mechanisms of arsenic release to the groundwater goethite with subordinate amounts of hematite were using mossbauer spectroscopy identified as the iron oxide minerals present in both types of sediment the release kinetics of fe as mn and po 4 from the sediment were investigated in leaching experiments with hcl and 10 mm ascorbic acid both at ph 3 from the river sediments most of the fe and as was mobilized by reductive dissolution with ascorbic acid while hcl released very little fe and as this suggests as to be associated with an fe oxide phase for oxidized aquifer sediment most fe was mobilized by ascorbic acid but here not much as was released however the reduced aquifer sediments contained a large pool of fe ii and as that is readily leached by hcl probably derived from an unidentified authigenic fe ii containing mineral which incorporates as as well extraction with ascorbic acid indicates that the river sediments contain both as v and as iii while the reduced aquifer sediment almost exclusively releases as iii the difference in the amount of fe ii leached from river and oxidized aquifer sediments by ascorbic acid and hcl was attributed to reductive dissolution of fe iii the reactivity of this pool of fe iii was quantified by a rate law and compared to that of synthetic iron oxides in the river mud fe iii had a reactivity close to that of ferrihydrite while the river sand and oxidized aquifer sediment exhibited a reactivity ranging from lepidocrocite or poorly crystalline goethite to hematite mineralogy by itself appears to be a poor predictor of the iron oxide reactivity in natural samples using the reactivity of synthetic fe oxides as a reference sediments were incubated both unamended and with acetate added and monitored for up to 2 months the river mud showed the fastest release of both fe and as while the effect of acetate addition was minor this suggests that the presence of reactive organic carbon is not rate limiting in the case of the river and aquifer sediments the release of fe and as was always stimulated by acetate addition and here reactive organic carbon was clearly the rate limiting factor the reduced aquifer sediment apparently can sustain slower but prolonged microbially driven release of as the highly reactive pools of fe iii and as in the river mud could be due to reoxidation of as and fe contained in the reducing groundwater from the floodplain aquifers that are discharging into the river deposition of the suspended mud on the floodplain during high river stages is proposed to be a major flux of as onto the floodplain and into the underlying aquifers

a review of high arsenic groundwater in mainland and taiwan china distribution characteristics and geochemical processes china is a typical high as region where 20 provinces have high as groundwaters among 34 provinces these groundwaters usually occur in both arid semiarid inland basins and river deltas in the inland basins mainly distributed in the northwest of china shallow groundwaters usually have high as concentrations in alluvial lacustrine or lacustrine sediment aquifers while high as groundwater mainly occurs in fluvial marine sedimentary aquifers in the river deltas which have been affected by transgression in both the inland basins and the river deltas high as groundwaters mainly occurring in reducing conditions are characterized by high fe and mn concentrations high ph and hco3 concentration and relatively low no3 and so42 concentrations although as contents are well correlated to fe mn contents in the aquifer sediments groundwater as concentrations are generally independent of sediment as contents redox processes microbe related reduction and desorption processes are the major geochemical processes for as enrichment in groundwaters in reducing conditions both reductive dissolution of fe oxides and reductive desorption of as are believed to result in as mobilization which would be catalyzed by indigenous microbes although decomposition of the low molecular weight organic matter during microbe metabolization would also release the colloid bound as into groundwater the cycling of colloidal as still needs to be further investigated during redox processes besides high ph and high hco3 lead to as desorption from adsorption sites in the aquifer systems however the contribution of competitive desorption to high as concentrations is still unknown and remains to be discovered relative to reductive dissolution of fe oxides especially in the inland basins

water masses and circulation in the surface layers of the caribbean at 66 w a meridional hydrographic section was made in august september 1997 at 66 w from the coast of venezuela to woods hole aboard the r v knorr in this report we concentrate on near surface measurements in the caribbean the data show two distinct water masses with different origins from approximately 14 n to puerto rico caribbean surface water and subtropical under water with their source in the north atlantic are found as previously observed from venezuela to approximately 13 n a less saline water mass with its source in the tropics and south atlantic is found within the southern portion of the section two different velocity patterns are observed namely an eastward flow with a subsurface maximum near the coast of venezuela and a surface intensified westward jet with velocities of 130 cm s 1 in midbasin

vertical distribution of bacterial populations associated with arsenic mobilization in aquifer sediments from the hetao plain inner mongolia to understand the mechanism of arsenic mobilization from sediment to groundwater mediated by microorganism vertical distribution of bacterial populations in aquifer sediments of the hetao plain inner mongolia was investigated by a two step nested pcr dgge and 16s rrna gene clone libraries combined with sediment geochemistry a borehole to 30 m depth was drilled and 11 sediment samples were collected lithological profile and different geochemical characteristics of sediments indicated a distinct transition of oxidizing reducing environment along the depth of the sediment core as iii and fe ii concentrations elevated progressively from 10 m simultaneously coupling with decrease of as v and fe iii concentrations implying that reductive dissolution of arsenic rich fe iii oxyhydroxides led to arsenic release results of dgge displayed that sediment samples with higher concentrations of total arsenic and total organic carbon had lower population diversity which suggested total arsenic concentrations were important to determine the population diversity of sediments bacterial communities of a sediment sample with the highest diversity and ratio of as iii to total as were dominated by aerobic and facultative anaerobic bacteria and belonged to alpha beta and gammaproteobacteria and firmicutes group most of the retrieved sequences were closely related to high arsenic resistance organisms sulfide thiosulfate oxidizers denitrifiers and aromatic hydrocarbon degraders thiobacillus distinctly predominated in clone library which suggested that arsenic might be released by oxidized dissolution of sulfide minerals coupled to arsenate reduction or nitrate reduction in anaerobic condition these data have important implications for understanding the microbially mediated arsenic mobilization in aquifers

factors affecting arsenic content of unconsolidated sediments and its mobilization in the ishikari plain hokkaido japan arsenic as contamination of groundwater is often caused by as leaching from geological formations this study focused on factors affecting as content in unconsolidated sediments by using three sediment cores in the ishikari plain hokkaido japan the geochemical properties of the sediments were characterized by the chemical and mineral compositions as well as leaching experiments and sequential extractions of as the results showed that higher as content of 4 9 mg kg was observed in peat layers with organic matter content 10 wt and that higher as contents deeper than 8 m below the surface were also observed the deeper sediments were likely to be formed in brackish water conditions due to lower weight ratios of organic carbon content to sulfur content c s 10 the results of the leaching experiments showed that as was mobilized at slightly alkaline region these indicate that the distribution of as depended on the organic content in the sediments and sedimentation condition and that the mobility of as in the sediment was affected by ph

mobilisation of arsenic and other trace elements in fluviolacustrine aquifers of the huhhot basin inner mongolia observed as concentrations in groundwater from boreholes and wells in the huhhot basin of inner mongolia northern china range between 1 g l 1 and 1480 g l 1 the aquifers are composed of quaternary largely holocene lacustrine and fluvial sediments high concentrations are found in groundwater from both shallow and deep boreholes as well as from some dug wells well depths ranging between 10 m and 400 m populations from the affected areas experience a number of as related health problems the most notable of which are skin lesions keratosis melanosis skin cancer but with internal cancers lung and bladder cancer also having been reported in both the shallow and deep aquifers groundwaters evolve down the flow gradient from oxidising conditions along the basin margins to reducing conditions in the low lying central part of the basin high as concentrations occur in anaerobic groundwaters from this low lying area and are associated with moderately high dissolved fe as well as high mn nh4 dissolved organic c doc hco3 and p concentrations many of the deep groundwaters have particularly enriched doc concentrations up to 30 mg l 1 and are often brown as a result of the high concentrations of organic acid in the reducing groundwaters inorganic as iii constitutes typically more than 60 of the total dissolved as the highest as concentrations tend to be found in groundwater with low so4 concentrations and indicate that as mobilisation occurs under strongly reducing conditions where so4 reduction has been an active process high concentrations of fe mn nh4 hco3 and p are a common feature of reducing high as groundwater provinces e g bangladesh west bengal high concentrations of organic acid humic fulvic acid are not a universal feature of such aquifers but have been found in groundwaters from taiwan and hungary for example the observed range of total as concentrations in sediments is 3 29 mg kg 1 n 12 and the concentrations correlate positively with total fe up to 30 of the as is oxalate extractable and taken to be associated largely with fe oxides the release of as into solution under the reducing conditions is believed to be by desorption coupled with reductive dissolution of the fe oxide minerals the association of dissolved as with constituents such as hco3 doc and p may be a coincidence related to the prevalent reducing conditions and slow groundwater flow but they may also be directly involved because of their competition with as for binding sites on the fe oxides the huhhot groundwaters also have some high concentrations of dissolved u up to 53 g l 1 and f up to 6 8 mg l 1 in contrast to as u occurs predominantly under the more oxidising conditions along the basin margins fluoride occurs dominantly in the shallow groundwaters which have na and hco3 as the dominant ions the combination of slow flow of groundwater and the young age of the aquifer sediments are also considered potentially important causes of the high dissolved as concentrations observed as the sediments are likely to contain newly formed and reactive minerals and have not been well flushed since burial

atmospheric events disrupting coastal upwelling in the southwestern caribbean 1 year round coastal upwelling is a prevalent phenomenon in the southwestern caribbean region driven by northeast trade winds this pattern can be disrupted during the boreal winter to spring transition by event scale departures in the pressure systems characterized by a change in wind direction to northward with the accompanying relaxation of coastal upwelling to study these poorly understood events regional atmospheric and data assimilative ocean modeling experiments were carried out for the period 4 march to 9 april 2003 and compared to shipboard observations this combined ocean atmosphere approach allowed us to study the evolution of a 3 day atmospheric disturbance affecting ocean currents and collapsing the upwelling pattern against the colombian coast along the guajira peninsula near 12 n the southward extension of the coastal upwelling which normally reaches 10 5 n was blocked by the warmer and slightly lower salinity waters of the cyclonic panama colombia gyre under typical conditions the ocean model and shipboard observations of temperature and salinity profiles were in good agreement with each other both at coastal and oceanic stations the presence of a low level westward wind jet was manifested in the atmospheric model simulation confirming that it promotes the guajira upwelling system however the jet vanishes under disturbed atmospheric conditions

arsenic iron and organic matter in sediments and groundwater in the pannonian basin hungary in the central part of the pannonian basin factors controlling the distribution of as in sediments and groundwater of the upper 500 m were studied in core samples the amounts of as fe and mn extractable with hydroxylamine hydrochloride nh2oh hcl in 25 acetic acid the proportion of the 0 063 mm size fraction and the sediment organic c corg contents were measured in the groundwaters concentrations of as humic substances and selected major chemical components were determined in most core samples extractable fe as feooh and corg are correlated but some samples have excess fe or organic matter in cases where either excess fe or excess organic matter is found the amount of as is also elevated the spatial distribution of as in the groundwater and the lack of a consistent correlation of as with a single component indicate that there is no single factor controlling the concentration of dissolved as over the entire study area the only consistent feature is enrichment of as relative to fe in the groundwater compared to the sediments this suggests that the dissolution of fe minerals which primarily adsorb as is not congruent in reducing conditions fe iii oxyhydroxides together with adsorbed as dissolve and siderite with little or no as precipitates when sub regions are separated and studied individually it can be shown that hydrogeological features of the sediments the proportions of fe minerals and sedimentary organic matter and the concentration of dissolved humic materials all influence the accumulation and mobilization of as the significance of the different mobilizing processes however and the mean concentration of as is different in the recharge through flow and discharge areas

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

caribbean current and eddies as observed by surface drifters abstract recent satellite tracked surface drifter trajectories were analyzed to describe the mean currents and eddies in the caribbean sea the structure of the caribbean current and its variability were determined from high resolution 1 2 degree maps of the mean velocity and eddy kinetic energy looping drifter trajectories were used to identify discrete cyclones and anticyclones and their characteristics were described and related to the structure of the mean flow the translation rate of eddies in different areas was found to be similar to the mean velocity of the local background flow fields suggesting that the eddies were largely advected by the background flow ten energetic anticyclones translated westward at 13 cm s in the venezuela and colombia basins these anticyclones tended to lie in two bands centered near 15 n and 17 n coinciding with two jets of the caribbean current the northern weaker jet contains water primarily from the north atlantic the southern stronger jet contains water from the tropical and south atlantic the anticyclones are thought to have formed in the eastern caribbean from the anticyclonic vorticity derived from north brazil current rings the ring vorticity enters the eastern caribbean through island passages and is probably amplified by the anticyclonic shear on the northern side of the jets southwest of cuba a cyclone anticyclone pair was observed to translate slowly 2 cm s westward into the yucatan current the cyclone was tracked for 10 5 months with four drifters making it the longest tracked of the caribbean eddies

geochemical evidence of the anthropogenic alteration of element composition in lacustrine sediments from wuliangsu lake north china abstract wuliangsu lake is located in the upper reaches of the yellow river and its catchment is found in the hetao basin one of the three largest irrigation districts in china a 56 cm length sediment core was collected from the south side of the lake geochronology radiometric methods using 137 cs and 210 pb were subsequently used to date the short sediment core the concentrations of elements al fe ca mg na k ti co v cr be ba sr cu pb zn mn ni and p were studied in the solid phase at each 1 cm section based on correlation analysis and principal component analysis four groups of elements were identified the first group included total p cu and mn which indicate anthropogenic activities such as agriculture industry and sewage effluents the second group included co pb and zn that were influenced by both anthropogenic and natural factors the third group consisted of ca and sr the concentration profiles of ca and sr displayed a negative correlation with the remaining elements al k fe mg be etc which comprised the fourth group that were mainly terrigenous in addition the enrichment factors efs for all elements used as a means of identifying and quantifying human interference was evaluated the efs for cu mn pb zn co and p showed significant variation finally with constrained clustering analysis of efs for cu mn pb zn co and p the stages of regional environment were orderly and objectively divided before the 1960s efs for heavy metals displayed relatively constant values suggesting a little human influence the increasing severity of heavy metal accumulation evidenced by enhancement of efs for heavy metals began to appear in the 1960s which corresponded to local environmental development and therefore reflects strengthened human impacts the efs of total phosphorus and heavy metals then increased rapidly especially at the beginning of the 21st century