interactions between sediment production and transport in the geometry of carbonate platforms insights from forward modeling of the great bank of guizhou early to middle triassic south china abstract carbonate platforms grow through the precipitation transport and final deposition of carbonate sediment out of seawater quantifying the relative contributions of initial production versus subsequent transport in determining the growth rates and geometries of platforms remains a significant challenge in this study stratigraphic forward modeling is used to quantify the roles of sediment production transport and deposition during each growth stage of a permian triassic carbonate platform with a complex growth history parameter optimization and sensitivity analysis show that within the range of reasonable values the morphology of the platform is most sensitive to sediment transport moderately sensitive to maximum carbonate production rate and least sensitive to the productivity depth curve the ramp to high relief steep sloped platform transition during early triassic time can be explained by any factor that limits sediment transport from shallow water areas of high production to the slope and basin reefs may play a role in limiting sediment transport on many platforms but other processes such as early marine cementation or carbonate production along the slope may be equally capable of yielding this shift in platform geometry in this particular case early lithification of ooid and skeletal shoals on the platform margin perhaps facilitated by unusually high carbonate saturation state of seawater may have inhibited sediment transport into the basin prior to the development of a reef on the platform margin later anisian progradation of the platform margin can be explained by the development of a slope factory rather than requiring increased sediment transport from the platform top the development of an escarpment margin in the ladinian is mainly influenced by accommodation in the slope profile created by antecedent anisian topography a general implication from the model results is that the growth of steep sloped carbonate platforms lacking slope factories may often be limited by transport of sediment from the platform top to accommodation on the slope rather than by the intrinsic production capacity of the platform top factory

salinity change in the subtropical atlantic secular increase and teleconnections to the north atlantic oscillation 1 recent studies comparing shipboard data between the 1950 s and the 1990 s have shown significant heterogeneous adjustments of the temperature salinity structure of the n atlantic ocean here we present proxy records of temperature and salinity from aragonite sclerosponge skeletons extending existing records of the salinity maximum waters smw of the n atlantic back to 1890 these proxy records show secular temperature increases of 1 6 2 0 c higher than published global averages and salinity increases of 0 35 0 5 psu smaller than short term secular trends recently measured salinity reconstructions vary more significantly on the decadal scale showing changes that are related to low frequency variations of the north atlantic oscillation nao on both secular and decadal time scales the records indicate significant thermohaline changes in the smw either via forcing at the surface or increasing depths of density surfaces in the bahamas

microstructure measurements along a quasi meridional transect in the northeastern atlantic ocean 1 this study presents vertical profiles of turbulence parameters obtained in the upper 100 m of the northeastern atlantic ocean along a transect from tropical permanently stratified waters to subpolar seasonally stratified waters in july august 2009 the focus is to fully characterize the vertical mixing along this transect for further studies related to phytoplankton and nutrient distributions derived values of temperature eddy diffusivity kt of temperature variance dissipation rate t and of turbulent kinetic energy dissipation rate e indicate a northward increase of turbulent mixing below the mixed layer in the northern stations where the wind stress is sufficiently high the vertical distributions of e in the mixed layer follow the wind stress scaling the related low wind scaling factors and the low values of e encountered at this cruise are in agreement with a strongly stratified upper water column at midday in summer

carbonate periplatform sedimentation by density flows a mechanism for rapid off bank and vertical transport of shallow water fines existing theories of off bank sediment transport cannot account for rapid rates of sedimentation observed in bahama bank and florida shelf periplatform environments analysis of the physical processes operating during winter cold fronts suggests that accelerated off bank transport of shallow water mud may be achieved by sinking off bank flows of sediment charged hyperpycnal super dense platform waters

the structure of red infrared scattergrams of semivegetated landscapes a physically based linear stochastic geometric canopy soil reflectance model is presented for characterizing spatial variability of semivegetated landscapers at subpixel and regional scales landscapes are conceptualized as stochastic geometric surfaces incorporating not only the variability in geometric elements but also the variability in vegetation and soil background reflectance which can be important in some scenes the model is used to investigate several possible mechanisms which contribute to the often observed characteristic triangular shape of red infrared scattergrams of semivegetated landscapes scattergrams of simulated semivegetated scenes are analyzed with respect to the scales of the satellite pixel and subpixel components

geochemical and petrographical characterization of fine grained carbonate particles along proximal to distal transects the origin of carbonate ooze particles is often poorly understood this is due to their polygenic origin and potential post depositional alteration here the outcome of a physical separation study with regard to different component classes of micritic carbonates is shown the focus is on grain size and morphology mineralogy and isotope signatures two contrasting proximal to distal transects were investigated 1 the miocene leeward margin of great bahama bank odp leg 166 and 2 the transition between the maiella platform and the umbria marche basin in central italy near the cenomanian turonian boundary in both case settings carbonate particles of biogenic origin include at least three groups of organisms i planktonic foraminifera ii calcareous nannofossils and iii fragments of unspecified neritic skeletal material two further particle types lack diagnostic structures and based on particle size and mineralogy are here referred to as iv macroparticles 5 20 m mainly xenomorphic and v microparticles 12 m mainly automorphic to sub automorphic macro and microparticles represent 50 to 80 of the carbonate phase in slope and toe of slope domains and share characteristic carbon and oxygen isotope signatures macro and microparticles are considered shallow water precipitation products subsequently exported into the slope and toe of slope domains macroparticles are probably related to the fragmentation of neritic skeletal components while microparticles point to inorganic and or bioinduced precipitation in the water column in some cases macro and microparticles may have an early diagenetic origin the identification of the origin of fine grained particles allows for a quantitative assessment of exported in situ and diagenetic carbonate materials in periplatform environments the data shown here represent an important step towards a more complete characterization of carbonate ooze and micrite

alpha and beta diversity of encrusting foraminifera that recruit to long term experiments along a carbonate platform to slope gradient paleoecological and paleoenvironmental implications abstract the spatial and temporal distribution and diversity of sediment dwelling foraminifera are reasonably well known but encrusting hard substrate dwelling foraminifera are little studied encrusting foraminifera are common in the world s oceans attached to floating debris or marine animals in the water column to living on rocks sand grains and organisms in benthic environments from shallow to deep marine regions with projected ocean acidification and warming conditions these important calcifying protists that comprise beaches buffer sediments and contribute to complex food webs are potentially in peril results indicate that calcifying foraminifera were the first to colonize experimental molluscan substrates within the first year in shallow habitats with colonization offshore in subsequent years agglutinated foraminifera become more common after one year species richness diversity remained relatively similar throughout the study but species turnover diversity was greatest within the first year and between the shelf slope break and deeper water following the thermocline and photic zone regions the equivalent of the shannon entropy index provided important information on diversity and community structure paleobathymetric distributions can be resolved after six years into four distinct foraminiferal distributional zones shallow shelf 15 m outer shelf 33 m shelf slope break 73 88 m and slope depths 213 m to 267 m some encrusting foraminifera are invasive settling in high numbers within the first year and increasing their abundance through the duration of the experiment a foraminiferan discorbis bertheloti was discovered to bioerode carbonate and is a potentially excellent paleobathymetric indicator for 15 33 m depths results differ from previously reported pioneer and climax foraminiferal communities documented for caribbean coral reefs because long term experiments reveal the spatial and temporal development and distribution of carbonate producing encrusting foraminifera in these climatically sensitive regions

periplatform drift the combined result of contour current and off bank transport along carbonate platforms hydroacoustic and sedimentological data from the western leeward flank of the great bahama bank document the interplay of off bank sediment export along slope transport and erosion which together shape facies and thickness distribution of slope carbonates the integrated data set depicts the combined product of these processes and allows formulation of a comprehensive model of a periplatform drift that significantly amends established models of carbonate platform slope facies distribution and geometry the basinward thinning wedge of the periplatform drift at the foot of the bank escarpment displays along slope and downslope variations in sedimentary architecture sediments are muddy carbonate sands that coarsen basinward the drift wedge has a pervasive cover of cyclic steps in zones of lower contour current speed depth related facies belts develop whereas strike discontinuous sediment lobes scarps and gullies characterize areas with higher current speed this understanding of the impact of currents on carbonate slope sedimentation has wider implications for seismic and sequence stratigraphic interpretation of carbonate platforms and for applied aspects such as hydrocarbon exploration

massive recrystallization of low mg calcite at high temperatures in hydrocarbon source rocks implications for organic acids as factors in diagenesis we document massive recrystallization of low mg calcite lime mudstone source rocks at moderately high temperatures in the smackover formation of mississippi this process was driven by organic acids produced during kerogen maturation and holds the implications for studies of primary migration of hydrocarbons secondary porosity generation in reservoirs and global environmental change this interpretation is based on contrasting the following petrographic and bulk rock geochemical characteristics of organic poor vs organic rich lime mudstones

production of hypersaline pools in shallow basins by evaporation 1 this paper incorporates a correction to the heat balance equation in the general ocean models by properly quantifying the sun s light that penetrates the ocean surface and reaches the bottom part of the light that hits the bottom in shallow pools of water gets absorbed depending on the albedo of the bottom and is reradiated as heat thus warming up the waters there significantly the light that is not absorbed gets reflected back up and a part of it is absorbed by the water constituents on its way up while the remaining light leaves the water surface it was found from our simulations that the temperatures attained by shallow pools depend upon the water depth and bottom albedo increased evaporation associated with such shallow water warming leads to the formation of hypersaline waters this natural salination is found to occur in the shallow basin near the andros island in the bahamas where the waters are less than 7 m deep the maximum salinity of these waters is as high as 46 psu in summer these hypersaline waters being denser than the nearby deep ocean advect down to depths of 50 m in summer and 75 m in winter

the effects of grain density variation on turbidity currents and some implications for the deposition of carbonate turbidites abstract sediment grains in carbonate turbidity currents vary greatly in size shape surface texture and density depending on the evolution of the source carbonate platform in time and space facies character and distribution may vary from traditional siliciclastic turbidite models not only because of the difference in composition but also because variation in grain properties influences flow and depositional behavior experimental gravity flows were generated to investigate one control on this variation the experiments used silicon carbide 3214 kg m 3 and glass ballotini 2650 kg m 3 with a similar grain size distribution in varying proportions to assess the influence of particle density on flow and sedimentation processes mixed particle density flows were more efficient than single particle density flows flow propagation was faster in flows with greater initial bulk density determined by grain density and suspended sediment concentration with mixed particle suspensions flow propagation velocity was maintained for longer due to the presence of low settling velocity particles as a result mixed particle density flows transported more sediment downstream compared to single particle density flows of similar initial suspended sediment volume concentration because of the wider range of grain types in carbonate turbidity currents they may more effectively transport coarse sand grade sediment to more distal sites in a marine basin compared to siliciclastic counterparts of equivalent initial volume this results in differences in bed and facies geometry and distribution

seismic architecture and seismic geomorphology of heterozoan carbonates eocene oligocene browse basin northwest shelf australia abstract seismic characterization of eocene oligocene heterozoan carbonate strata from the browse basin northwest shelf of australia defines marked progradation of nearly 10 km stratal terminations and stacking subdivide the succession into mappable seismic units stratal architecture and seismic geomorphology varies systematically through the succession individual surfaces discerned by toplap onlap and truncation outline sigmoidal to tangential oblique clinoforms with heights of ranging from 350 to 650 m and maximum gradients between 8 and 18 sigmoidal clinoforms can include aggradation in excess of 200 m prograde more than 500 m and have slopes characterized by inclined wavy to discontinuous reflectors that represent ubiquitous gullies and channels in contrast the overlying tangential oblique clinoforms include downstepped shelf margins limited on shelf aggradation the associations of shelf aggradation shelf margin progradation and slope channeling within sigmoidal seismic units and the less marked progradation and channeling within tangential oblique seismic units contrast with the classic sequence model in which sediment delivery to the slope and pronounced progradation is favored by limited shelf accommodation this distinct divergence is interpreted to reflect the prolific heterozoan production across the shelf during periods of rising and high base level when the shelf is flooded perhaps enhanced by downwelling comparison with purely photozoan systems reveals similarities and contrasts in seismic stratigraphic heterogeneity and architecture interpreted to be driven by distinct characteristics of heterozoan sedimentary systems

mixing at camarinal sill in the strait of gibraltar during the gibraltar experiment in 1985 1986 observations of shear stratification microstructure and acoustic backscatter revealed a complex mixing regime at camarinal sill in the strait of gibraltar the mixing is forced by strong semidiurnal tidal currents and weaker but more steady baroclinic flows flows are characterized as outflow or inflow nearly equivalent to westward or eastward rising water at gibraltar coincides with outflow at all depths we observed two modes of outflow at the sill in may 1986 the transition layer separating atlantic and mediterranean water was between 0 75 mpa and 1 mpa when we sampled east of the sill near neap tide the transition turned down just before reaching the sill crest where the flow became critical increasing shear soon destabilized the transition producing billows which grew to 30 75 m on the west flank of the sill the overturning generated intense turbulence with peak dissipation rates e exceeding 10 2 w kg 1 this turbulence rapidly thickened the transition from z 30 50 m east of the sill to z 130 150 m within 1 2 km west of the sill from the rate of thickening we estimate the rate of formation of new transitional water during neap tide as 0 8 1 2 105 m3 s 1 this outflow mode did not release eastward propagating internal bores when outflow turned to inflow but the inflow did appear to arrest the deep outflow in may the largest average dissipation rate over and just west of the sill had the same magnitude as estimates of the net energy lost by adjustment of velocity and mass across the sill during outflow other averages are smaller than the energy loss presumably because the limited sampling severely underestimates the average dissipation rate during outflow strong shears were observed to rise to 100 times those in the background internal wave field however probably owing to spatial offsets between the ship s acoustic doppler current profiler and our tethered free fall profiler the only statistically significant correlations were found between overturning scales measured directly and those estimated from e in the same profile we observed the other outflow mode in october 1985 when we profiled over the sill near spring tide and the transition was east of the sill centered near 1 5 mpa after encountering the sill the transition rose sharply and remained within 10 20 m of the surface across the sill plunging steeply downward just past the west edge of the sill this was accompanied by intense turbulence and at least one rebound of the transition we did not observe release of eastward propagating bores when inflow turned to outflow but observations by armi and farmer 1988 in april 1986 found bores released at spring tide in regimes similar to the one we observed in october 1985

sedimentary dynamics and high frequency sequence stratigraphy of the southwestern slope of great bahama bank abstract new geophysical data from the leeward slope of great bahama bank show how contour currents shape the slope and induce re sedimentation processes along slope segments with high current control drift migration and current winnowing at the toe of slope form a deep moat here the slope progradation is inhibited by large channel incisions and the accumulation of large mass transport complexes triggered by current winnowing in areas where the slope is bathed by weaker currents the accumulation of mass transport complexes and channel incision is rather controlled by the position of the sea level large slope failures were triggered during the mid pleistocene transition and mid brunhes event both periods characterized by changes in the cyclicity or the amplitude of sea level fluctuations within the seismic stratigraphic framework of third order sequences four sequences of higher order were identified in the succession of the upper pleistocene these higher order sequences also show clear differences in function of the slope exposure to contour currents two stochastic models emphasize the role of the contour currents and slope morphology in the facies distribution in the upper pleistocene sequences in areas of high current influence the interplay of erosional and depositional processes form a complex facies pattern with downslope and along strike facies alterations in zones with lower current influence major facies alternations occur predominately in downslope direction and a layer cake pattern characterizes the along strike direction therefore this study highlights that contour currents are an underestimated driver for the sediment distribution and architecture of carbonate slopes

high frequency cyclicity milankovitch and millennial scale in slope apron carbonates zechstein upper permian north east england the upper permian zechstein slope carbonates in the roker formation zechstein 2nd cycle carbonate in north east england consist of turbidites interbedded with laminated lime mudstone studies of turbidite bed thickness and relative proportion of turbidites percentage turbidites in 20 cm of section reveal well developed cyclicities consisting of thinning upward and thickening upward packages of turbidite beds these packages are on four scales from less than a metre up to 50 m in thickness assuming that the laminae of the hemipelagic background sediment are annual allows the durations of the cycles to be estimated in addition counting the number and thickness of turbidite beds in 20 cm of laminated lime mudstone which is approximately equivalent to 1000 years each lamina is 200 m gives the frequencies of the turbidite beds the average thicknesses and the overall sedimentation rates through the succession for 1000 year time slots figures obtained are comparable with modern rates of deposition on carbonate slopes the cyclicity present in the roker formation can be shown to include milankovitch band ca 100 kyr short eccentricity ca 20 kyr precession and ca 10 kyr semi precession cycles and sub milankovitch millennial scale cycles 0 7 to 4 3 kyr eccentricity and precession scale cycles are related to highstand shedding and relative sea level change caused by milankovitch band orbital forcing controlling carbonate productivity the millennial scale cycles which are quasi periodic probably are produced by environmental changes controlled by solar forcing i e variations in solar irradiance or volcanic activity most probable here are fluctuations in carbonate productivity related to aridity humidity and or temperature changes precession and millennial scale cycles are defined most strongly in early transgressive and highstand parts of the larger scale short eccentricity cycles the duration of the roker formation as a whole can be estimated from the thickness of the laminated lithotype as ca 0 3 myr

impact of carbonate producing biota on platform architecture insights from miocene examples of the mediterranean region abstract different types of carbonate platforms formed in the mediterranean during the miocene low angle homoclinal types of ramp distally steepened ramps flat topped platforms and reef rimmed shelves the critical differences between these platforms result from differences in the capacities of the carbonate systems to accumulate sediments above hydrodynamic base level ecologically controlled accommodation the various depositional profiles and facies belt distributions resulted from the interplay between different sediment production and redistribution processes and the internal architectures resulted from the response of each type of platform to changes in accommodation heterogeneities driven by high frequency sea level cycles are maximized in platforms ruled by shallow water euphotic framework dominated production and minimized in low angle ramps where sediment resulted from aphotic and oligophotic carbonate production in the mediterranean region there is no direct relationship between type of platform and global temperature as shown by the coeval occurrence of different platforms in similar latitudinal settings although temperature is a key limiting factor other paleoceanographic factors such as trophic resources may have also been along with biological evolution important factors influencing different types of carbonate producing biotas

mapping bathymetry and depositional facies on great bahama bank satellite imagery and an extensive set of water depth measurements have been used to map and critically evaluate the magnitude and patterns of bathymetry across great bahama bank descriptions of previously collected sediment samples were combined with satellite imagery to map and refine the interpreted distribution of surficial carbonate sediments depositional facies data reveal that 60 of great bahama bank lies in 5 m or less of water the deep portion occurs mainly in a generally east west trending area in the southern portion of the platform the re evaluation of the facies reveals that great bahama bank is essentially a very grainy platform with muddier accumulations primarily in the lee of andros island this area of great bahama bank also experiences currents related to an excursion of the florida current onto the platform top possibly enhancing sediment mud production through the generation of whitings sediment equivalents to mudstones wackestones and mud rich packstones cover 8 5 and 14 respectively of the platform top whereas sediment equivalents to mud poor packstones grainstones and rudstones account for 20 45 and 3 of the surface area boundstones reefs were not specifically mapped in this study due to the resolution of the mapping there is a poor relationship between the occurrence of the depositional texture and water depth in that the grainier sediment types are abundant across the full range of water depths the most abrupt lateral facies changes portrayed on the facies maps are observed leeward of islands areas which also hold the highest diversity in facies type the majority of the islands on the platform align with the north west south east strike of the platform margin and these islands in turn exert control on the shape and orientation of facies belts that develop in proximity to them for this reason regions of the platform that contain principal islands host facies belts that align with the principal axis of the platform whereas for regions lacking islands the facies belts adopt an east west trend consistent with prevailing winds and currents there is a clear trend that the wide southern portion of the platform hosts the most continuous expanses of grain rich sediments

new insights into the morphology and sedimentary processes along the western slope of great bahama bank new high quality multibeam and seismic data image the western slope of the great bahama bank and the adjacent floor of the straits of florida the extensive survey reveals several unexpected large and small scale morphologies these include bypass areas channel leveelobe systems gullied slopes and products of slope instabilities at various scales including long slump scars at the lower slope and mass transport complexes that extend 30 km into the adjacent basin floor the toe of the slope is irregularly covered with deep water carbonate mounds the abundance of the individual morphological features varies from north to south from 26 00 n to 25 20 n the slope is dissected by numerous deep canyons that abruptly end southward where the slope is characterized by a smooth lower portion and small regularly spaced furrows in its upper part further south two long 25 50 km scars document instability at the lower slope one of these scars is the source area of a large mass transport complex in addition to this large scale feature several types of gravity induced sedimentary processes are revealed most of the morphologies and inferred processes of this carbonate system are similar to those observed in siliciclastic systems including mass transport complexes gravity currents initiated by density cascading and overspilling channeled turbidity currents for the first time a clear asymmetric channel levee system has been identified along the slope suggesting similitude in sorting processes between carbonate and siliciclastic systems and enhancing the reservoir bearing potential of carbonate slopes notable differences with siliciclastic systems include the lack of connection with the shallow and emerged part of the system i e bank top and the small size of the sedimentary system 2012 geological society of america

variability of cold water coral mounds in a high sediment input and tidal current regime straits of florida cold water coral mound morphology and development are thought to be controlled primarily by current regime this study however reveals a general lack of correlation between prevailing bottom current direction and mound morphology i e footprint shape and orientation as well as current strength and mound size i e footprint area and height these findings are based on quantitative analyses of a high resolution geophysical dataset collected with an autonomous underwater vehicle from three cold water coral mound sites at the toe of slope of great bahama bank the three sites 80 km2 total have an average of 14 mounds km 2 indicating that the great bahama bank slope is a major coral mound region at all three sites living coral colonies are observed on the surface of the mounds documenting active mound growth morphometric analysis shows that mounds at these sites vary significantly in height 1 to 83 m area 81 to 6 00 000 m2 shape mound aspect ratio 0 1 to 1 and orientation mound longest axis 0 to 180 the autonomous underwater vehicle measured bottom current data depict a north south flowing current that reverses approximately every six hours the tidal nature of this current and its intermittent deviations during reversals are interpreted to contribute to the observed mound complexity an additional factor contributing to the variability in mound morphometrics is the sediment deposition rate that varies among and within sites at most locations sedimentation rate lags slightly behind mound growth rate causing mounds to develop into large structures where sedimentation rates are higher than mound growth rates sediment partially or completely buries mounds the spatial distribution and alignment of mounds can also be related to gravity mass deposits as indicated by geomorphological features for example slope failure and linear topographic highs in the three dimensional bathymetry in summary variability in sedimentation rates current regime and underlying topography produce extraordinarily high variability in the distribution development and morphology of coral mounds on the great bahama bank slope

quaternary slope development of the western leeward margin of the great bahama bank abstract to date work on the great bahama bank s western leeward margin has centred chiefly on seismic scale expressions of carbonate sequences and systems tracts however periplatform slope sediments also exhibit very well developed cyclicity on scales of decimetres to several metres it is these small scale high frequency cycles within the larger scale facies successions of the quaternary which form the main topic of this paper previous studies have shown that the small scale cycles correlate to the orbitally forced high frequency sea level changes therefore these cycles should indicate how sea level has affected the slope development and thus platform margin evolution during this period through detailed high resolution sequence stratigraphy of the great bahama bank s leeward margin obtained via 18o isotope and mineralogical xrd analyses confined by u th dating and nannofossil bioevents a greater understanding of the bedding geometries within the pleistocene holocene seismic sequences and clues as to the nature of the slope development has been achieved the high resolution seismic profiles indicate that since the plio pleistocene change in geometry in which the great bahama bank developed into a rimmed platform continued steepening and subsequent progradation of the leeward margin has typified slope development during the quaternary which is described as an accretionary slope however on the basis of our observations we conclude that only the early to lower middle pleistocene section isotope stages 45 20 and the holocene isotope stage 1 of the leeward margin is accretionary this indicates that a degree of erosion and or by passing has occurred on the leeward margin since the lower middle pleistocene isotope stage 19 during the first part of this period isotope stages 19 12 erosion and or by passing occurred in the middle to lower slope regions and toe of slope by the end of the upper middle to late pleistocene phase isotope stages 11 2 erosion also occurred on the upper slope this erosion by currents at the toe of slope and oversteepening of the upper and middle slopes have led to back cutting upslope and resulted in the progressive retreat of the toe of slope towards the platform to the east however the rise in sea level since the last glacial maximum to its present day level has allowed high productivity on the platform top during the holocene and the deposition of a thick sediment wedge on the slope and sedimentation across the entire leeward flanks this has led to the redevelopment of an accretionary slope and continued westward progradation of the great bahama bank s western leeward margin

response of tropical cyclone tracks to sea surface temperature in the western north pacific abstracta set of short term experiments using a regional atmospheric model ram were carried out to investigate the response of tropical cyclone tc tracks to sea surface temperature sst in the western north pacific for 10 selected tc cases occurring during 2002 07 a warm and a cold run are performed with 2 and 2 k added to the ssts uniformly over the model domain respectively the cases can be classified into three groups in terms of recurvature recurved tracks in the warm and cold runs a recurved track in the warm run and a nonrecurved track in the cold run and nonrecurved tracks in both runs commonly the warm run produced northward movement of the tc faster than the cold run the rapid northward migration can be mainly explained by the result that cyclonic circulation to the west of the tc is found in the steering flow in the warm run and it is not in the cold run the beta effect is also activated under the warm sst environment for the typical tc cases a linear baroclinic model experimen

observations of upper ocean boundary layer dynamics in the marginal ice zone 1 vertical profiles of turbulent kinetic energy dissipation and small scale hydrography were collected in the upper ocean boundary of both ice covered and ice free stations in the marginal ice zone of the barents sea in spring 2005 together with shipboard wind measurements and current profiles the mixed and mixing layer dynamics are studied during the survey shear production by the stress at the surface or under the ice dominated large upward turbulent heat fluxes 300 500 w m 2 were calculated for the mixing layers overlying the warm atlantic water which compared well with those obtained from an independent parameterization at the top of the pycnocline corresponding heat fluxes were 10 20 w m 2 significant stabilizing buoyancy fluxes were estimated for ice drift stations owing to the melting of ice in response to the large heat fluxes the mean dissipation profile in the ice free reference station agreed with the constant stress wall layer scaling within 30 on the contrary the observed dissipation profiles were enhanced in the upper half of under ice mixing layer or within 2 5 times the assessed pressure ridge keel depth deeper in the mixing layer the profiles relaxed toward the wall scaling the variability of dissipation in the mixed layer was better captured by the shear production profile when local friction speed was used together with a mixing length profile modified by buoyancy fluxes significant correlations were found between dissipation integrated over the mixing layer and work done by stress under the ice and the wind work at 10 m height the low correlation between the mixed layer depth and length scale for neutral conditions significantly increased when the reduction in the mixing length due to buoyancy fluxes was accounted for the mixing depth is observed to be strongly correlated with the outer neutral planetary length scale

holocene millennial to centennial carbonate cyclicity recorded in slope sediments of the great bahama bank and its climatic implications a 38 m long sediment core md992201 retrieved from a water depth of 290 m from the leeward margin of the great bahama bank gbb 25 53 49 n 79 16 34 w has been investigated for changes in aragonite content the core covers the mid to late holocene the past 7230 yr sediment lightness l values was used as a proxy for aragonite content based on a high linear correlation r 0 93 between the x ray diffraction derived aragonite content and l values the resulting time resolution of the l values derived aragonite content ranges from 1 yr at the base of the core to 4 yr at the top detailed time series analysis using monte carlo singular spectrum analysis and spectral analysis lomb scargle fourier transform identifies the presence of seven signals with varying amplitudes and wavelengths that could be traced throughout the past 5500 yr during the first 1600 yr of sedimentation the aragonite record is dominated by the initial flooding of the flat topped gbb superimposed on a multimillennial signal related to holocene sea level changes a millennial scale fluctuation and five quasi periodic oscillations were detected 1 3 2 kyr 500 600 yr 380 yr 260 yr 200 yr and 100 yr period comparisons with other proxies e g tree ring 14c 10be and 18o in ice cores provides information on the origin and dynamics of the individual signals the analysis shows that the 200 yr and 100 yr signals can be attributed to solar forcing the 260 yr 380 yr and the 500 600 yr quasi periodic signals are found to be of climatic origin whereas the millennial scale fluctuations remain enigmatic although solar forcing mechanisms seem likely the data show that variability of solar output as well as past oceanographic and atmospheric changes have modulated the mid to late holocene climate which in turn controlled sediment input variations found in the holocene wedge leeward of the gbb although these periplatform sediments have a rather uniform appearance they still contain a large variety of subtle sedimentary variations

controls on grain size patterns in periplatform carbonates marginal setting versus glacio eustacy the importance of grain size as a fundamental property controlling other physically derived properties is well known recent grain size studies on periplatform sediments of the caribbean and western north atlantic have shown that grain size variability is coupled with changes in carbonate platform productivity and export in response to pleistocene holocene glacio eustacy these findings showed that periplatform sediments are dominated by fine grained material during sea level highstands and coarser material during sea level lowstands this paper addresses the question of grain size patterns in periplatform settings and their relationship to glacio eustacy furthermore it considers whether these patterns are applicable to different types of margin settings accretionary erosional here existing data pleistocene holocene from the accretionary western leeward margin of great bahama bank odp leg 166 and new data from the erosional eastern windward margin odp leg 101 are used the results show that the grain size patterns of both margins are controlled by late neogene sea level fluctuations the accretionary leeward margin sediments indicate the same grain size pattern as previously described in the literature however the erosional windward margin shows a reverse pattern with coarser sediments in interglacials and finer deposits in glacials this proposes that the leeward margin grain size pattern is controlled by the productivity export mode of the platform this is indicated by the platform top derived fine muds transported off bank to form a thick sediment wedge on the low angled slope during interglacials in contrast on the windward margin the sediment flux pattern is controlled by the impact of mass transport processes this is indicated by the increased occurrence of turbidites during interglacials that might be more frequent at this time because the steep angled erosional slope is less apt for the deposition of excess fine material this material is eroded and or bypasses the slopes and is redeposited in the periplatform basin setting

carbonate slope morphology revealing sediment transfer from bank to slope little bahama bank bahamas new high quality multibeam and high resolution seismic data reveal new observations on sediment transfer and distribution and margin morphometrics in the uppermost slope of northeastern little bahama bank between 20 and 300 m water depth the echofacies backscatter facies show an alongslope sediment distribution forming successive strips the upper part of the uppermost slope corresponds to the alternation of several submerged coral terraces and escarpments that could be related to late quaternary sea level variations the terraces could either be related to periods of stagnating sea level or slow down in sea level change and therefore increased erosion by waves or periods of accelerated sea level rise since the last glacial maximum terraces could therefore be related to coral construction and drowing the medium part corresponds to the marginal escarpment a steep cemented area the lower part of the uppermost slope shows a discontinuous holocene sediment wedge with varying thickness between 0 and 35 m it is separated from the upper part by a zone of well cemented seafloor associated with the marginal escarpment passing cold fronts result in sediment export caused by density cascading the associated sediment fall out and convective sedimentation can generate density currents that form this wedge and eventually flow through linear structures on the upper slope the survey reveals the presence of recently active channels that extend over the entire uppermost slope and interrupt the wedge the channels connect shallow tidal channels to submarine valleys connected to the proximal part of canyons they directly feed the canyons with platform derived sediment forming low density turbidity currents and could supply the deepest part of the system with coarse grained sediment directly exported from the carbonate platform

the frasnian famennian boundary interval in the south polish moravian shelf basins integrated event stratigraphical approach abstract the late devonian mass extinction event near the frasnian famennian f f boundary has been analysed using conodont biostratigraphy and biofacies sedimentology magnetic susceptibility and geochemistry in reference sections of the south polish moravian shelf holy cross mountains cracow and brno areas high resolution biostratigraphic study revealed difficulties in the precise recognition of this natural stage boundary but confirmed the occurrence of a major third order sequence boundary in the f f transition in an active synsedimentary tectonic setting marked by erosional discontinuities hardgrounds and brecciation or omission surfaces conclusive evidence of an extraterrestrial impact has not been found among earth bound factors the main devastating role in the shelf habitats is ascribed to fluctuating anoxia and or nutrient dynamics in a disturbed greenhouse climatic setting the long term facies changes were determined by a conspicuous break in carbonate production accompanied by replacement of mature stromatoporoid coral reefs by pioneer shelly crinoid banks microbial mounds and localised oolitic bars the key f f passage interval was marked by intermittent but generally accelerated periplatform ooze debris input and severe storm events as well as by probably highly fluctuating oxygenation and biological overproduction best manifested in radiolarian silicisponge and cephalopod acmes eutrophication phenomena at least partly stimulated by various hydrothermal and volcanic processes were one of the major biogeochemical processes during this climax of the late devonian biotic crisis however significant oceanographic perturbations were also linked with the onset of the transgressive hypoxic upper kellwasser event still within the latest frasnian linguiformis zone i e well before the f f conodont collapse implied variations in the redox state of seawater through the kellwasser timespan probably in regionally highly variable temporal scales are in agreement with recent palaeoecological and biogeochemical inferences in particular suggesting recovering oxygenation just prior to the f f boundary in the other laurussian intrashelf basins all the data support a long time multicausal earth bound crisis instead a worldwide cosmic catastrophe

u and th concentrations and isotope ratios in modern carbonates and waters from the bahamas the short residence times of th and pa in seawater make them very responsive to changes in the ocean environment we use a new multi ion counting technique to make th and pa isotope measurements in seawaters from a near shore environment in which oceanic chemical tracers are not overwhelmed by terrestrial inputs the bahamas an unusual feature of the bahamas setting is the shallow depth of water residing on the bank tops these waters have significantly lower 232th 230th 10 000 than those immediately adjacent to the banks 24 000 31 000 and a 231pa 230th near the production ratio 0 1 the change in 232th 230th and 231pa 230th on the bank tops is explained by almost quantitative removal of th and pa by scavenging and their replacement with a mixture of 230th and 231pa alpha recoiled from the underlying carbonates together with th from dust dissolution analysis of a water profile in the tongue of the ocean which separates the great and little bahama banks allows us to trace the movement of bank top water to depth a distinct minimum in both 232th 230th 13 000 and 231pa 230th 0 5 is observed at 430 m and is interpreted to reflect density cascading of bank top water with entrained carbonate sediment these results suggest that th and pa can be used as water mass tracers in near shore environments uranium concentration measurements on the same waters demonstrate that u is conservative across a range in salinity of 2 psu with a concentration of 3 33 ppb at a salinity of 35 the incorporation of u and th isotopes into marine carbonates has also been assessed by analyzing carbonate samples from the same location as these bahamas waters such incorporation is critical for u th geochronology u isotope analyses demonstrate that seawater 234u averages 146 6 and does not vary by more than 2 5 o and that carbonates capture this value additional high precision measurements 1 o on modern carbonates confirm that all oceans have identical 234u modern marine carbonates are shown to have 232th 230th ratios that reflect the local seawater in which they formed

whiting related sediment export along the middle miocene carbonate ramp of great bahama bank modern aragonite needles are present all along the modern leeward margin of great bahama bank odp leg 166 while middle miocene sediments contain needles only in more distal areas sites 1006 and 1007 in contrast to the rimmed flat topped platform topography during the plio pleistocene the miocene great bahama bank morphology is a carbonate ramp profile this might imply a different location and precipitation type for miocene aragonite needles in this study aragonite needles in miocene sediments were isolated using a granulometric separation method furthermore the isolation of the various carbonate components enables the identification of primary versus diagenetic components the miocene aragonite needles are concentrated in the finest granulometric sediment fractions 12 m the fraction specific geochemical analyses 13c 18o and sr elemental abundance represent useful tools to assess the possible sources of the aragonite mud the geochemical variation of the fractions rich in pristine aragonite needles and the characteristics of the needle morphology point to whiting phenomena as the main sediment source and algal fragmentation as a minor component both components indicate shallow water environments as the main sediment source area ramp top related fine grained particles now present at distal sites were likely exported as suspended material similar to present day transport mechanisms the scarcity of needles at proximal sites is probably linked to hydrodynamic processes but dissolution and recrystallization processes cannot be excluded the granulometric separation approach applied here enables a better characterization of the finest carbonate particles representing an important step towards the discrimination between primary and diagenetic fine grained components

scale interaction between typhoons and the north pacific subtropical high and associated remote effects during the baiu meiyu season the interaction between typhoons and the north pacific subtropical high and the associated remote impact on east asian and north pacific anomalous weather during the baiu meiyu season have been investigated using the japanese long term reanalysis project data aided by the japan meteorological agency climate data assimilation system the typhoons that appeared in july have been categorized into two primary tracks the hainan island course hc and the okinawa island course oc a typhoon gives rise to negative absolute vorticity advection along its eastern periphery which locally reinforces the western ridge of the north pacific subtropical high whereas the resultant anomalous high stimulates the westward northward migration of the hc oc typhoon through its combination with the background flow a combined effect of the typhoon and its induced anomalous anticyclonic circulation increases the transportation of moisture into the baiu meiyu frontal zone in the vicinity of japan over the east china sea and the sea of japan northward or northeastward moisture flux is pronounced along the western periphery of the typhoon induced anticyclonic circulation anomaly in the hc category triggering heavy rainfall on central japan s sea of japan coast similar remote effects also operate in the oc category which is responsible for the occurrence of extremely heavy rainfall along the pacific coast of western japan when an oc typhoon approaches the asian jet it is capable of giving rise to anticyclonic vorticity within the jet leading to the downstream development of stationary rossby wave packets via the north pacific waveguide

morphometric analysis of plunge pools and sediment wave fields along western great bahama bank abstract a systematic assessment of morphometric parameters of over 200 plunge pools along the steep escarpment base of western great bahama bank and 2000km2 of sediment wave fields of upslope migrating cyclic steps documents the importance of cascading density currents for sedimentation on the slope the abrupt downslope termination of the holocene mud wedge with the cyclic steps shows that strike parallel bottom currents interacting with the off bank currents are responsible for slope sediment distribution the plunge pools and sediment waves were generated by density cascading and both are related to a hydraulic jump caused by two gradient changes along the slope profile the bedforms highlight both the erosional and depositional nature of this current regime which is controlled by slope gradient and the directional confinement by either grooves on the steep escarpment or gullies on the middle to lower slope the 20 m deep plunge pools are ellipsoidal with an average width of 211 m and length of 283 m but variations between 80 360 m and 100 650 m for width and length occur they are caused by an average gradient break of 16 on the cemented upper slope gradient breaks of as low as 2 are reported to be sufficient to scour a plunge pool like the ones in the study area but higher gradient breaks between 10 and 20 are quite common for consistent plunge pool development a second gradient break further down slope changes flow conditions for the generation of cyclic steps with asymmetric waveforms of 4 m high average in large wave fields in the entire the study area orientation is mainly orthogonal to the main slope direction but wave lengths and sinuosity vary depending on the morphologic location of the wave field the comparison with sediment wave fields with similar geometries or in similar environments shows that flow reconstruction based on the wave height and wave length alone along with a characterization of sediment grain size however yields non unique results and is site specific

constraining initial 230th activity in incrementally deposited biogenic aragonite from the bahamas the 230th content of subsurface bahamas seawater has been estimated from incrementally deposited aragonite skeletons of sclerosponges using u series age models which imply syndepositional incorporation of 230th first order age models assuming constant growth rate and zero initial 230th activity display an average surface age of 63 18 y despite the fact that the surfaces of the organisms were known to be alive at the time collection in the 1990s a knowledge of the initial 230th activity is necessary to incorporate the surface age constraint into an age model in the bahamas this approach estimates an initial 230th 232th activity ratio of 4 3 1 1 when applied to several individuals of the caribbean sclerosponge ceratoporella nicholsoni these results differ from the same approach applied to previous work on jamaican sclerosponges accreting aragonite in an environment closer to crustal sources and with less carbonate substrate we report new measurements of jamaican sclerosponge suggesting initial activity ratios of 230th 232th of 1 albeit with a high amount of uncertainty indicating a regional difference in initial thorium activities the estimates of initial 230th 232th activity ratios in the bahamas are similar to the dissolved ratio rather than the particulate ratio and can be explained by mixing of open ocean water and bank top surface water however no information regarding temporal changes in the amount of initial 230th 232th activity available for incorporation into biogenic aragonite can be constrained using this approach growth rates do not change after correction for initial thorium and they display an inverse relationship with depth although this paper deals uniquely with sclerosponge aragonite it is likely that the approach can be used on any incrementally deposited biogenic aragonite provided information is known a priori about the first order growth model and there is evidence that initial thorium incorporation is representative of ambient environment rather than individual physiology

modeling discrete forest anisotropic reflectance over a sloped surface with an extended goms and sail model topographic effects on canopy reflectance play a pivotal role in the retrieval of surface biophysical variables over rugged terrain in this paper we proposed a new canopy anisotropic reflectance model for discrete forests geometric optical and mutual shadowing and scattering from arbitrarily inclined leaves model coupled with topography gosailt which considers the effects of slope aspect geotropic nature of tree growth multiple scattering and diffuse skylight gosailt simulated areal proportions of four scene components i e sunlit crown shaded crown sunlit background and shaded background were evaluated using the geometric optical model for sloping terrains gost model the canopy reflectances simulated by gosailt were validated against two reflectance data sets discrete anisotropic radiative transfer dart simulations and wide angle infrared dual model line area array scanner widas observations compared with a horizontal surface the forest canopy reflectance over a steep slope 60 is significantly distorted with absolute relative bias values of 0 048 79 60 and 0 056 12 02 for the red and near infrared nir bands respectively the gosailt simulated component areal proportions show close agreements with gost moreover gosailt simulations have high overall accuracy red band coefficient of determination r 2 0 96 root mean square error rmse 0 003 and mean absolute percentage error mape 3 91 and nir band r 2 0 78 rmse 0 019 mape 3 94 when compared with the dart simulations these extensive validations indicate good performances of gosailt in canopy reflectance simulations over sloped surfaces

holocene atlantic climate variations deduced from carbonate periplatform sediments leeward margin great bahama bank a marine sediment core from the leeward margin of great bahama bank gbb was subjected to a multiproxy study the aragonite dominated core md992201 comprises the past 7230 years in a decadal time resolution and shows sedimentation rates of up to 13 8 m kyr aragonite mass accumulation rates age differences between planktonic foraminifera and aragonite sediments and temperature distribution are used to deduce changes in aragonite production rates and paleocurrent strengths aragonite precipitation rates on gbb are controlled by exchange of carbonate ions and co2 loss due to temperature salinity conditions and biological activity and these are dependent on the current strength paleocurrent strengths on gbb show high current velocities during the periods 6000 5100 years bp 3500 2700 years bp and 1600 700 years bp lower current speeds existed during the time intervals 5100 3500 years bp 2700 1600 years bp and 700 100 years bp bahamian surface currents are directly linked to the north atlantic atmospheric circulation and thus periods with high low current speeds are proposed to be phases of strong weak atmospheric circulation

high resolution simulation of the circulation in the bahamas and turks and caicos archipelagos abstract we present the first high resolution simulation of the bahamas and turks and caicos archipelagos implemented with the regional oceanic modeling system roms our model resolves tides and our simulation consists of two nested grids of respectively 4 and 2 km horizontal resolution this oceanic region is constituted of the juxtaposition of very large and shallow banks and very deep basins our modeling study shows that the dominant influence is the salinity from the sub tropical gyre which varies latitudinally with seasons less salty surface waters entered the archipelago from september to november from the north and through the old bahama obc and the north west providence nwpc channels as the western atlantic saline waters moved south saltier atlantic waters arrived from the south in december and moved north till the next fall this salinity flux is mitigated by the atmospheric forcing on the banks as well as the water temperature which varied diurnally what modified the water density causing this water to be unique to the banks yielding its own seasonality as seen in their sst the banks were colder in winter and warmer in summer than their surrounding waters fronts were formed at every ebb tide in winter spring and fall however the influence of bank waters on the surrounding waters was shown to be limited because of the dominant influence of the large scale flow and of the local production of water masses by wind and cyclone driven upwelling bank waters were contained at the front where they mixed with the surrounding waters as shown by the short time presence of the fronts local wind in addition to the tide was also shown to be a significant forcing which is responsible for some of the short scale variability 5 30 days in florida current transport the nwpc the obc the windward passage wp and the antilles current ac finally the study also confirmed the mesoscale eddy influence at seasonal scales 100 days on the ac transport as well as on the fc through a possible leakage of eddy flux through the nwpc a similar influence was found south of the archipelago where mesoscale eddy could also influence wp transport

overflow into the deep caribbean effects of plume variability the deepest connection between the eastern caribbean and the atlantic is over the jungfern grappler sill complex at 1815 m depth through these gaps flows the sole source of water for the deep caribbean presumably balanced by diffusively driven upwelling elsewhere in the basin fourteen month long moored observations at the sills in 1991 1992 reveal a mean transport of 0 11 0 05 sv 1 sv 106 m3 s l of atlantic water colder than 0 3 965oc flowing into the caribbean one quarter of which comes over the previously unmeasured grappler sill this is about twice the transport seen in previous shorter experiments the overflow is highly episodic with 10 events per year the range of overflow density is comparable to the total vertical strati fication of the deep caribbean a numerical stream tube model of the overflow plume is run with 13 different initial conditions representing the observed range of overflow strength and density results indicate that much of the overflow only penetrates to 2200 3000 m depth and was dense enough to descend to the bottom of the caribbean only 1 of the time combined plume model results are used to drive a model of the basin stratification a steady balance is found to be possible with small diapycnal diffusivity in the basin between 0 1 and 0 6 cm2 s 1 the reason for the small diffusivity is that the stratification is essentially built in place by the different detrainment depths and so less diffusive transformation is needed below a depth of 1815 m the eastern caribbean is topog raphically isolated from the rest of the worlds ocean figure l a middepth water flows from the atlantic through anegada pass 1915 m into the virgin islands basin vib figure lb a small intermediate basin between the atlantic and caribbean the source water for the inflow is upper north atlantic deep water unadw which lies between depths of 1200 2000 m along the western boundary of the north atlantic leaman and harris 1990 show the freon maximum at 26 5on associated with labrador sea water nominally the source of unadw to be at 1200 m considerably shallower than the anegada sill depth however labrador sea water still appears to form the bulk of what flows into the deep caribbean atlantic water at that depth is also influenced to a lesser degree by the high salinity mediterranean ouflow water as is apparent from the contour map of salinity on the 3 8oc potential temperature surface by worthington and wright 1970 from the vib water flows through jungfern pass 1815 m and nearby grappler pass 1710 m as reported by fratantoni et al 1997 forming a dense overflow plume that cascades into the deep caribbean throughout this paper

dense saline plumes in exuma sound bahamas cold dense plumes have been associated with coral killoff on tropical shelves as well as with sediment movement from banks to the deep basins adjacent to shallow banks this paper presents evidence that plumes of dense salty water generated over shallow banks entrain ambient water rather than descending intact to a density compensation level as has sometimes been assumed and that plumes can spread laterally distances of tens of kilometers from their source in exuma sound dense salty water appears to be formed year round by cooling or by evaporation over shallow banks the water is forced by tidal currents through the channels between islands onto the narrow shelves of exuma sound where it likely moves as gravity currents the gravity currents entrain basin water as they cross the shelf and cascade over the steep shelf edge into exuma sound after which they are advected by ambient currents around the sound a numerical streamtube model was used to explore early details of plume evolution the model predicts that the plumes entrain 2 6 5 0 parts ambient water particularly as they traverse the gently sloping shelf the resulting loss of density contrast means that the model plumes reach their density level in exuma sound at relatively shallow depths 50 95 m just below the base of the mixed layer the final depth of modeled plumes is relatively consistent with observed plume depths which vary seasonally 75 m in early winter to 45 m in summer depending on the depth and density characteristics of the seasonal mixed layer over the sound observed plume thickness ranges from 40 m in winter to 20 30 m in summer final salinity values exceed 36 8 practical salinity units final density ranges from sigmat 23 75 to 24 5 plume depth vertical structure and longevity are shown to depend on upper ocean mixing processes such as convection and wind mixing

high resolution stratigraphic forward modeling of a quaternary carbonate margin controls and dynamic of the progradation abstract the relationships between the margin sedimentary regime and the platform progradation are studied using forward stratigraphic numerical simulations on the leeward western prograding margin of the great bahama bank gbb during the quaternary 1 7 0 ma the corresponding sedimentary regime in the slope and the platform is well known from the odp leg 166 and bahamas drilling project wells located along the western line seismic transect however the sedimentary regime on the margin is not well established the coral reefal margin observed before between 1 7 and 0 8 ma in the well clino is not active anymore at present day and the holocene sedimentary regime is geometrically unable to account alone for the progradation this study is based on three 2d high resolution forward stratigraphic numerical modeling experiments with the software dionisosflow that include the platform margin and slope domains on the western line section in the same sedimentary models the results are compared to the six sedimentary cores and to the present day bathymetry in order to identify the more realistic scenario the three experiments test different models of carbonate sediment production and transport experiment 1 shows that the highstand shedding of the fine grained uncemented platform production is unable to reproduce the progradation and the present day profile experiments 2 and 3 incorporate cemented facies in the margin with the best results obtained with the cemented marginal wedges produced in experiment 2 during platform emersion from these results a high resolution interpretation of the margin seismic section is proposed this study shows that the platform progradation can be decoupled from the highstand shedding of the fine grained platform production it is dependent on the accumulation in front of the steep margin of coarse or cemented material before 0 8 ma this corresponds to the coral reef identified in clino the transition after 0 45 ma to 100 kyr large eustatic cycles with total platform flooding created two distinct marginal regimes 1 during platform flooding aggrading accumulation of non skeletal sands and 2 during platform emersion prograding cemented marginal wedges produced in situ

petrography and environmental controls on the formation of phanerozoic marine carbonate hardgrounds early marine seafloor lithification of carbonate sediments leads to the formation of hardgrounds and is known from rocks as old as the proterozoic hardground surfaces however are more commonly recorded in the phanerozoic sedimentological archive while ecological studies of hardground biota abound the environmental and physico chemical parameters leading to the development of seafloor lithification remain in many cases poorly understood and documented this paper reviews published evidence on the petrography mineralogy and geochemistry of phanerozoic carbonate hardgrounds within a process oriented context of their environmental controls hardgrounds typically develop in warm and shallow agitated tropical waters that are saturated with respect to caco3 but are also reported from hemi pelagic to bathyal realms and from cool water temperate settings a range of early marine cement types are documented from present day hardgrounds whereas preserved cement fabrics and related mineralogies are less diverse in early phanerozoic hardgrounds carbonate hardgrounds are widespread during calcite sea periods e g ordovician and cretaceous as opposed to some preservation bias ancient aragonite seas e g permian and triassic obviously the relation between seawater chemistry and hardground abundance and attributes is not an easy one here the concept of aragonite versus calcite seas serves as a first order template for the sake of a structured discussion whereas modern aragonite mode oceans document a significant diversity in spatial and bathymetric seawater properties this spatio temporal complexity is perhaps reflected in the scarce record of calcite sea hardgrounds from the devonian or paleogene rock record contrasted by the abundance in aragonite holocene and recent seas holocene hardgrounds allow for the direct assessment of rates of and reasons for early subaquatic lithification and in most cases escaped subsequent non marine diagenetic overprint conversely studies of ancient hardgrounds are often biased by early biological and mechanical erosion the degree of diagenetic overprint and tectonic to orogenic processes the formation distribution and physical properties of hardgrounds depend on the global climatic context greenhouse icehouse modes on sea level changes on ocean stratification on the spatial extent of epicontinental seas and carbonate depositional environments and on the spatially different mineralogies and rates of carbonate production the fabrics and mineralogies of early hardgrounds cement seem to substantially hinge on variations in atmospheric co2 thus the application of lessons from modern to ancient hardground case examples is not straightforward a holistic model explaining the full variability of controls on submarine hardground formation and their cement petrography throughout the phanerozoic is as yet lacking a more critical view on secular changes in hardground formation patterns is clearly needed future work should rely on the combination of sedimentological stratigraphic palaeoecological petrographic and geochemical approaches specific emphasis should be given to time intervals triassic carboniferous cambrian etc where the bulk of reported case studies is at best scarce

convectively driven turbulent mixing in the upper ocean abstract two experiments were performed to study the characteristics of turbulence in convective mixed layers in the upper ocean in the first a diurnal convective mixed layer developed in the bahamas under the influence of the cycle of daytime solar heating and nighttime evaporative cooling the mixed layer reached as deep as 100 m each night and restratified each day in the second the mixed layer of a warm core gulf stream ring deepened from less than 50 m to more than 150 m in a little more than a day when subjected to rapid cooling during a cold air outbreak although individual profiles of the rate of viscous dissipation of turbulent kinetic energy had considerable spatial and temporal variability the mean dissipation profiles were similar to those in convecting atmospheric boundary layers the is established by the surface buoyancy flux jb0 jb0 0 61 and 0 72 in the bahamas and ring data respectively compared with 0 64 in convecting atmospheric mixed layers the mean profiles decre

nutrient control of the global occurrence of isolated carbonate banks the growth and origin of the world s isolated carbonate banks are as yet not completely understood this paper presents a comparison of the areas depths and latitudinal distribution of the world s carbonate banks these are then compared with chemical parameters of seawater in the upper mixed zone of the oceans and at depth the results allow large scale inferences to be made on the interacting controls on bank growth and distribution the data support the hypothesis that nutrient rich waters commonly control bank depth and size

modeling the effects of buoyancy on the evolution of geophysical boundary layers a simple modeling based on the imperial college k e turbulence description is shown to be capable of describing the highly anisotropic phenomena associated with the strong buoyancy effects encountered in upper ocean and atmospheric boundary layer environments both diurnal stratification and transition to buoyant mixing from that driven by wind shear are described in considerable detail provided that the modeling of the turbulent prandtl number and of the buoyant generation term in the e model equation are evaluated in a suitably realistic and consistent way the resulting model equations are suitable for simulating the evolution of the ensemble averaged properties of the oceanic mixed layer in response to a specified history of interfacial shear stress and heat flux the model is tested by comparing the predicted mixed layer evolution with the dissipation rate measurements of shay and gregg

momentum and energy balance of the mediterranean outflow field data taken in the gulf of cadiz have been analyzed to describe some aspects of the momentum and energy balance of the mediterranean outflow a crucial component of the momentum balance is the total stress entrainment stress and bottom drag which has been estimated from a form of the bernoulli function evaluated from density and current observations for the first 60 km west of the camarinal sill the outflow was confined within a narrow channel on the continental shelf at about 70 km downstream the outflow crossed over the shelf slope break and began to descend the continental slope the buoyancy force increased substantially and the outflow underwent a geostrophic adjustment albeit one heavily influenced by mixing and dissipation the current direction turned 90 degrees to the right at a near inertial rate in this region the estimated geostrophic velocity greatly underestimated the actual current and the estimated curvature rossby number was about 0 5 current speeds were in excess of 1ms 2 1 and the total stress was as large as 5 pa the entrainment stress estimated independently from property fluxes reached a maximum of about 1 pa or considerably smaller than the inferred bottom stress by about 130 km downstream the current was aligned approximately along the local topography the current amplitude and the estimated stress were then much less about 0 3 m s21 and 0 3 pa the entrainment stress was also very small in this region well downstream of the strait this slightly damped geostrophic flow continued on to cape st vincent where the outflow began to separate from the bottom bottom stress thus appears to be a crucial element in the dynamics of the mediterranean outflow allowing or causing the outflow to descend more than a kilometer into the north atlantic in the regions of strongest bottom stress the inferred drag coefficient was about 2 2 12 3 10 23 depending upon which outflow speed is used in the usual quadratic form entrainment stress was small by comparison to the bottom stress but the entrainment effect upon the density anomaly was crucial in eroding the density anomaly of the outflow the observed entrainment rate appears to follow roughly a critical internal froude number function

possible refugia for reefs in times of environmental stress this paper investigates the refuge potential of 1 upwelling areas 2 coral areas at medium depth and 3 offshore bank and island reefs in a scenario of increased global warming and thus increased sea surface temperature sst and increased solar uv radiation 1 observations on coral health and water temperature in the subtropical atlantic eleuthera and cat island bahamas and indian ocean sodwana bay south africa suggest a link between cool water delivered by upwelling and coral health after the 1998 bleaching event caused by strong sst anomalies coral health and recovery from the previous year s bleaching was significantly better on the narrow southern cat island shelf 70 of corals healthy where the presence of cold water was observed which was attributed to small scale upwelling than on the wide northern eleuthera shelf 44 of corals healthy where downwelling of hot bank waters was believed to have damaged corals in south africa regular short term upwelling events in five summers reduced sst to well below bleaching level 2 in the northern red sea safaga bay and in south africa sodwana bay wide areas with either coral frameworks or non framework communities exist calculations show that if the top 10 m 20 m of the ocean became inhospitable to corals still 50 4 17 5 of the coral area would remain intact in the red sea and 99 40 in south africa 3 offshore bank and island reefs investigated in the turks caicos and mouchoir banks and grand and little cayman showed high rates of mortality and coral diseases the most remote sites mouchoir bank were not the healthiest refuge areas appear to exist in 1 and 2 but in 3 only if vigorous water circulation is encountered

an estimation of water origins in the vicinity of a tropical cyclone s center and associated dynamic processes to clarify the time evolution of water origins in the vicinity of a tropical cyclone tc s center we have simulated typhoon man yi july 2007 in our case study using an isotopic regional spectral model the model results confirm that the replacement of water origins occurs successively as the tc develops and migrates northward over the western north pacific it is confirmed that in this case a significant proportion of total precipitable water around the cyclone center comes from external regions rather than the underlying ocean during the mature stage of a tc similar features can also be seen in the proportion of each oceanic origin to total condensation indian ocean south china sea and maritime continent water vapors begin to increase gradually at the developing stage and reach their peak at the decay stage when the tc approaches southwestern japan these remote ocean vapors are transported to the east of the cyclone via the moisture conveyor belt a zone characterized by distinct low level moisture flux that stretches from the indian ocean to the tc and are further supplied into the inner region of the tc by inflow within the boundary layer associated with its secondary circulation since it takes time to undergo these two dynamic processes the delayed influence of remote ocean vapors on the tc appears to become evident during the mature stage

gaining insight into clipperton s lagoon hydrology using tritium historical descriptions of the clipperton lagoon appear to converge on the fact that it became isolated from the surrounding ocean around 1858 since then because of the high precipitation rate which largely exceeds evaporation in this region of the eastern tropical pacific a brackish lens has formed on top of the saline oceanic waters in 1980 literature data show that the thickness of this water body was reaching 14 m during the 2005 etienne s clipperton expedition we collected lagoon water on two vertical profiles salinity 18 o and tritium analyses were performed on these samples with the objective of gaining further insight into the lagoon hydrology and age of the deep waters the upper 15 m were characterized by low salinities 5 4 0 2 and 18 o and tritium values typical of local precipitation at depth waters had salinity and 18 o similar to oceanic surface waters but with low tritium concentrations hence pointing to quite isolated waters representing a remnant of marine waters when the lagoon was still communicating with the ocean at lagoon closure the excess of precipitation over evaporation raised the lagoon level thus creating a hydraulic pressure head which favored salt expulsion through the permeable walls of the atoll a simple geohydrological modeling of this salt expulsion process based on darcy s law describes reasonably well the time evolution of the brackish lens tritium is used to discuss the main physical processes potentially involved in the slow ventilation of the halocline and deep saline layer including vertical diffusion sinking of salty surface water intrusions and deep horizontal exchange through fissures in the limestone these different mechanisms give reasonable results which are all compatible with available salinity and isotopic data 18 o and tritium and therefore are all plausible candidates unfortunately the lack of a detailed description of the vertical tritium profile in the halocline between 15 m and 20 m precludes any further quantification of their respective role in the ventilation process

application of a transient reduced gravity plume model to the denmark strait overflow a hydrostatic reduced gravity two dimensional primitive equation numerical model for the simulation of transient bottom arrested gravity plumes was developed by adopting an algorithm from a wadden sea model a model that simulates the wetting and drying of mud flats sand banks etc with a movable lateral boundary the vertically integrated nonlinear rotational model accounts for the dissipation of momentum due to bottom friction and for the entrainment of water mass properties from a spatially structured but stagnant ambient water body it predicts the temporal and spatial evolution of the flow field and the water mass modification within a gravity plume that descends on an arbitrary topography previous model investigations considered a laterally integrated streamtube whereas our model resolves the plume horizontally in the streamtube approach it was assumed that the plume descends in a stationary almost geostrophic balance modified only by bottom drag and entrainment the results of this model demonstrate that this balance may be disturbed whenever the plume encounters topographic disturbances which for the initial intruding phase in particular accounts for its highly transient character the model results are in good agreement with theoretical and laboratory investigations and with observations as is demonstrated by some basic test experiments an application to the overflow of dense water through the denmark strait is presented

seismic reflection imaging of shallow oceanographic structures 1 multichannel seismic mcs reflection profiling can provide high lateral resolution images of deep ocean thermohaline fine structure however the shallowest layers of the water column z 150 m have remained unexplored by this technique until recently in order to explore the feasibility of shallow seismic oceanography so we reprocessed and analyzed four multichannel seismic reflection sections featuring reflectors at depths between 10 and 150 m the influence of the acquisition parameters was quantified seismic data processing dedicated to so was also investigated conventional seismic acquisition systems were found to be ill suited to the imaging of shallow oceanographic structures because of a high antenna filter effect induced by large offsets and seismic trace lengths and sources that typically cannot provide both a high level of emission and fine vertical resolution we considered a test case the imagery of the seasonal thermocline on the western brittany continental shelf new oceanographic data acquired in this area allowed simulation of the seismic acquisition sea trials of a specifically designed system were performed during the aspex survey conducted in early summer 2012 the seismic device featured i four seismic streamers each consisting of six traces of 1 80 m ii a 1000 j sig sparker source providing a 400 hz signal with a level of emission of 205 db re 1 pa 1 m this survey captured the 15 m thick 30 m deep seasonal thermocline in unprecedented detail showing images of vertical displacements most probably induced by internal waves

carbonate shedding and sedimentary cyclicities of a distally steepened carbonate ramp miocene great bahama bank depositional geometries as imaged in seis mic lines logging data and quantitative petrographic data were used to analyse the slope and toe of slope deposits of the miocene distally steepened carbonate ramp of great bahama bank the shedding pattern along the slope of this ramp is more complex than it is along the slope of the pliocene pleistocene flat topped carbonate platform compositional changes and compositional trends of periplatform sediments correlate with the positions of geophysically defined sequence boundaries two types of depositional sequences occur the first sequence is characterised by laterally traceable sequence internal reflections whereas the second type contains major intrasequen tial incisions erosional incisions and sedimentary infills of these canyons by turbidites formed during sea level lowstands as is indicated by the composition of the turbidites having a mixture of shallow water and pelagic particles highstand turbidites are charac terised by more extensive laterally traceable geome tries and by the occurrence of abundant shallow water particles in contrast to highstand turbidites shed from the pliocene pleistocene flat topped platform shal low water components in highstand turbidites of the miocene ramp are of skeletal origin the stacking pat tern of the periplatform deposits is controlled by sea level fluctuations four orders of sea level changes are distinguished third order cycles are delimited by sequence boundaries and fourth 100 000 a order cycles govern the bundling of turbidites into packages fifth 40 000 a and sixth 23 000 a order cycles are recorded in the background sediments and resolvable with spectral analysis

dynamical processes of transfer at the sea surface abstract this review describes the dynamical processes of transport from and immediately below the sea surface particularly those which involve convergence and the separation of flow and which result in the renewal of surface water at horizontal scales ranging from millimeters to hundreds of meters turbulence at or near the sea surface derives from several processes breaking waves and the bubbles they may produce precipitation and spray langmuir circulation and thermal convection and turbulence which is internally generated by shear interest in the subject derives from the requirements to predict air sea fluxes of heat momentum and gases to develop climate models to interpret satellite images of the sea surface including those of ship wakes and to predict upper ocean structure including mixing layer depth in models of phytoplankton blooms and acoustic propagation the general effect of subsurface turbulence on the sea surface and the effects of surfactants is described and each process is discussed in turn laboratory experiments and theoretical studies have contributed particularly to the understanding of the interaction of vortices and turbulence with the surface and to the consequences of breaking waves they point to the development of instability in the flow ahead of steep waves carrying parasitic capillary waves which may contribute to the onset of flow separation on the leading face of the waves and the development of a rotor or roller below the wave crest shown most clearly in the pattern of streamlines in a frame of reference moving forward with the wave the conditions near the flow separation line on the wave surface ahead of the rotor may be similar to those produced by vortices approaching a free surface detailed observation of breaking waves at sea is lacking but some progress has been made using acoustics to detect the clouds of subsurface bubbles formed by the larger breakers and the depth to which they penetrate the possible importance of three dimensional effects in breaking waves is discussed and a conjectural sketch of the surface flow field and the surface separation and reattachment pattern following a plunging breaker is described recent observations show elevated levels of turbulence close to the sea surface the depth of the layer in which this occurs is shown to be consistent with information derived from sonar studies of the depth of bubble clouds the observed frequency of breaking waves and laboratory observations of breaking waves rain is known to knock down the sea reducing the frequency and intensity of breaking waves the precise mechanics of the phenomena are uncertain but an enhancement of near surface turbulence and the damping of short surface gravity waves has been observed in laboratory experiments langmuir circulation temperature ramps and convection all associated with coherent structures are processes which mix the upper ocean although their relative importance is unknown connections between studies with quite disparate motivations are found to help provide descriptions of the upper ocean processes and estimates of the time scale of surface renewal associated with each of the processes identified many quantities being transferred across the sea surface appear to be transported by dynamical processes of scale much smaller than that of the dominant surface waves although their subsequent diffusion in the mixing layer may be strongly influenced by the larger scale processes further careful measurements in the laboratory and at sea are required to quantify the fluxes associated with the processes and to relate them to external parameters such as wind speed

periplatform ooze in a mixed siliciclastic carbonate system vaca muerta formation argentina abstract thick carbonate mud successions and marl limestone alternations are often found in periplatform environments the sources of these fine grained sediments and the processes that govern their accumulation and distribution in the basin are frequently a matter of debate this case study from a mixed siliciclastic carbonate succession in the neuquen basin argentina relates the origin of the carbonate dominated intervals to shelfal carbonate production the tithonian early valanginian basinal strata vaca muerta formation contains several carbonate rich intervals at different stratigraphic levels the thickest of these intervals is the mid late tithonian los catutos member in sierra de la vaca muerta this wedge shaped package of micritic limestones and intercalated marls thins basinwards proximal distal variations and cyclic partitioning in facies and geochemical proxies indicate highstand shedding and a periplatform origin for the los catutos member the proposed source is a coeval 20 m thick pure carbonate interval located 50 km south of the sierra de la vaca muerta within the mixed siliciclastic carbonate shelf facies of the picun leufu formation younger carbonate rich intervals in the center of the basin puerta curaco area show similar characteristics to the distal portion of the los catutos member and are also interpreted as periplatform deposits but sourced from carbonate shelves farther east the high sedimentation rates of the los catutos member require an efficient mechanism other than tides and winds to deliver significant amounts of fine grained carbonate sediment to the basin this mechanism is envisioned to be sediment charged hyperpycnal flows cascading from the platform to the basin analogous to what is observed in modern carbonate systems the occurrence of periplatform ooze in different stratigraphic levels of the siliciclastic dominated vaca muerta formation demonstrates that off shelf transport and distribution of carbonate mud in the basin are also common processes in mixed clastic carbonate environments

new insights on coral mound development from groundtruthed high resolution rov mounted multibeam imaging abstract currents play a vital role in sustaining and developing deep water benthic habitats by mobilising food and nutrients to otherwise relatively barren parts of the seabed where sediment supply is significant it can have a major influence on the development and morphology of these habitats this study examines a segment of the belgica mound province ne atlantic to better constrain the processes affecting a small sized cold water coral cwc mound habitat and conversely the hydrodynamic influence of cwc mounds on their own morphological development and surroundings here we utilise rov mounted multibeam rov video data and sediment samples to investigate current processes mound morphology density and development detailed mapping shows that the area may have the highest density of coral mounds recorded so far with three distinct mound types defined based on size morphology and the presence and degree of distinct scour features a residual current of 36 40 cm s 1 is estimated while large scour features suggest low frequency high magnitude events these 3 mound types are i smaller mounds with no scour ii mounds with scour in one to two distinct directions and iii larger mounds with mound encircling scour the differing mound types likely had a staggered initiation where younger mounds preferentially developed near clusters of pre existing mounds given the high density of these small cwc mounds we support the hypothesis that over time this clustering may eventually lead to these mounds coalescing into larger coral mound features

density cascading off shelf sediment transport evidence and implications bahama banks abstract suspended sediment concentrations in shelf waters are often appreciable but sediments on their own rarely contribute enough density to cause suspension currents to transport them offshelf however sediment charged hyperpycnal high density waters are often generated over continental shelves because of the same set of air sea interactions intense heat and moisture flux responsible for thermohaline production and circulation of deep ocean water masses we propose the term density cascading to describe the processes by which hyperpycnal waters are released from shelf areas and together with entrained sediments sink to their compensation level in the adjacent ocean density cascading probably involves a range of physical processes from pelagic draping of slopes and basins with shelf muds to initiating turbidity currents capable of scouring canyons and plunge pools sediment bypassing of slopes and deposition of sands in deep basins thermodynamic air sea interactions can generate hyperpycnal water at all latitudes therefore density cascading has important implications not only to the sedimentology of modern carbonate platforms such as the florida shelf and bahama banks and stratigraphy in ancient limestones but also to offshelf sediment flux in siliciclastic environments

sedimentary dynamics along carbonate slopes bahamas archipelago hydroacoustic and sedimentological data in the santaren channel covering both the leeward slope of great bahama bank and the windward slope of cay sal bank allow new insights into carbonate platform slope sedimentation the data document the interplay between depositional and erosive processes on both slopes through time and provide information on the current regime and its influence on the slope sedimentary processes this study emphasizes the diversity and complexity of the slope morphology and the sediment distribution of the youngest high frequency sequence which has developed since the last glacial maximum the processes triggering slope failures and the formation of channels and gullies differ on both slopes at the leeward slope of the great bahama bank extensive slope failures occurred primarily during sea level lowering following an interglacial these slope failures created a slope morphology that channelizes the exported platform sediments during the subsequent highstand at the windward slope of cay sal bank contour currents and the local tectonic regime are responsible for slope failures during sea level lowstands downwelling induces turbidity currents the interaction of turbidity and contour currents leads to the formation of a system of furrows and slope parallel sediment ridges the discovered heterogeneities in slope sedimentation improve the understanding of carbonate slope sedimentation and provide implications for sequence stratigraphic interpretation of carbonate platform slopes

the geosail model a simple addition to the sail model to describe discontinuous canopy reflectance abstract the scattering from arbitrarily inclined leaves sail model was combined with the jasinski geometric model to simulate canopy spectral reflectance and fraction of absorbed photosynthetically active radiation fapar for discontinuous canopies this model is called the geosail model tree shapes are described by cylinders or cones distributed over a plane spectral reflectance and transmittance of trees are calculated from the sail model to determine the reflectance of the three components of the geometric model illuminated canopy illuminated background and shadowed background although the geosail model is relatively simple calculations of canopy reflectance and fraction of intercepted photosynthetically active radiation fipar compared well with measurements collected in field experiments in forests in minnesota and oregon

geometric optical bidirectional reflectance modeling of a conifer forest canopy a geometric optical forest canopy model that treats conifers as cones casting shadows on a contrasting background explains the major anisotropies in bidirectional reflectance measurements of a conifer forest canopy taken from the literature the model uses parallelray geometry to describe the illumination and viewing of conifers as three dimensional cones cones are randomly placed and overlap freely cone size height is distributed lognormally and cone form described by the apex angle of the cone is a negative exponential function of height the cones are first presumed to be solid dark gray lambertian objects located on a lighter gray lambertian background to add realism translucence is added and light is allowed to pass through cones with negative exponential attenuation both computer simulation and analytical closed form expressions are implemented the results show a good qualitative agreement with the directional reflectance measurements of the conifer stand indicating that the three dimensional nature of the canopy is a key factor in determining its directional reflectance

large scale vapor transport of remotely evaporated seawater by a rossby wave response to typhoon forcing during the baiu meiyu season as revealed by the jra 55 reanalysis the modulation of large scale moisture transport from the tropics into east asia in response to typhoon induced heating during the mature stage of the baiu meiyu season is investigated using the japanese 55 year reanalysis jra 55 aided by a rayleigh type global isotope circulation model icm we highlighted the typhoons that migrate northward along the western periphery of the north pacific subtropical high and approach the vicinity of japan anomalous anticyclonic circulations to the northeast and southeast of typhoons and cyclonic circulation to their west become evident as they migrate toward japan which could be interpreted as a rossby wave response to typhoon heating these resultant anomalous circulation patterns form moisture conveyor belt mcb stretching from the south asian monsoon region to east asia via the confluence region between the monsoon westerlies and central pacific easterlies the icm results confirm that the well defined nature of the mcb leads to penetration of the indian ocean south china sea philippine sea and pacific ocean water vapors into western japan the typhoons have the potential to accumulate large amounts of moisture from distant tropical oceans through the interaction of their rossby wave response with the background flow in the case of a typical typhoon the total precipitable water around the typhoon center as it approaches japan is maintained by the moisture supply from distant oceans rather than from the underlying ocean which indirectly leads to the occurrence of heavy rainfall over western japan

southern ocean winter mixed layer austral winter 1986 observations from the polarstern along the greenwich meridian from the ice edge to the antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation incorporation of weddell deep water wdw into the winter mixed layer responsible for this undersaturation also introduces heat and salinity into the surface layer which strongly influences the mixed layer sea air exchanges and sea ice formation processes the total wdw transfer into the mixed layer averages 45 myr 1 implying a residence time for the surface water of 2 5 years the associated winter heat flux is 41 w m 2 which limits ice thickness to about 0 55 m agreeing quite well with observations the air temperatures during the cruise are just sufficient to remove the wdw heat input in the presence of observed ice thickness and concentration this suggests that the sea ice cover and wdw heat input into the mixed layer are in approximate balance by midwinter the annual heat flux from wdw to the surface layer and hence into the atmosphere is estimated as 16 w m 2 extrapolation of the greenwich meridian wdw entrainment value to the full circumpolar 60 70 s belt yields total up welling of 24 106 m3 s 1 similar extrapolation of the heat flux value gives a circumpolar total of 2 8 1014 w as a consequence of circulation topography interaction the maud rise water column stands out as an anomaly relative to the surrounding region with a significantly more saline and dense mixed layer below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m this uplifting is believed to be a response of the upstream flow encountering the rise increased upstream flow would be expected to increase maud rise upwelling and the dependent salinity density of the mixed layer slight increases in the mixed layer density could trigger a convective mode and generation of a polynya it is hypothesized that spin up of the weddell gyre s barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over maud rise

ventilation time scales of the north atlantic subtropical cell revealed by coral radiocarbon from the cape verde islands we present coral and sclerosponge based reconstructions of the 14c content in north atlantic dissolved inorganic carbon dic during the last 100 years from the subtropical cells stcs these waters are sensitive to the dynamics of the shallow overturning meridional circulation that transports heat and water masses from the subtropics to the tropics we use these records to investigate the circulation patterns of the off equatorial upwelling regions of the stcs which are not well understood coral and sclerosponge skeletons provide long time series of ocean dic 14c content a tracer of oceanic circulation effectively extending the observational record back in time sclerosponge data from the bahamas were used to extend the existing subtropical 14c time series to the 21st century coral 14c data from the cape verde islands 1890 2002 captured the 14c signature of water brought to the surface in the off equatorial regions of the stc present near the west african coast we observe a unique postbomb trend at cape verde that is similar to the upwelling regions in the pacific and we interpret this trend as the result of the slow penetration of bomb 14c into the interior ocean as part of the stc circulation using a multibox mixing model we constrain the time history of bomb 14c in the eastern tropical atlantic and we estimate a 20 year time scale for ventilation of the thermocline in this area of the ocean the similarity between the atlantic and pacific 14c based records of upwelling suggests that both are caused by bomb 14c penetration rather than more complex explanations that invoke changes in thermocline depth e g related to el nino southern oscillation variability or changes in the strength of the subtropical cells our results offer constraints for models of tropical ocean circulation and anthropogenic co2 uptake that attempt to reproduce the characteristics of the shallow wind driven circulation in the atlantic

gravity currents descending a ramp in a stratified tank this paper describes experiments and numerical simulations of a gravity current flowing down a ramp in a tank stratied in two layers we study the dynamics of the conguration for dierent densities of the gravity current and dierent ramp angles the experiments show that waves of large amplitude can be generated easily and that depending on the density of the gravity current the initial gravity current splits into a gravity current along the interface of the stratied layers and a gravity current along the bottom of the tank we also describe numerical simulations which give results in agreement with the results of the experiments and enable us to study three fluid congurations with wider ranges of density than is possible in the laboratory

carbonate mounds in the santaren channel bahamas a current dominated periplatform depositional regime abstract new hydroacoustic data high resolution multichannel seismic reflection data ctd casts and sampling document the dominance of bottom currents and the occurrence of carbonate mounds in the santaren channel off great bahama bank and cay sal bank based on these data sets three types of carbonate mounds have been identified in water depths between 285 and 685 m their distribution is strongly related to the present current regime bank driven sediments are caught up by the currents and redeposited mainly in the channel center resulting in the accumulation of giant confined drifts flanked by moats the moats at the banks toe of slope are formed by a southward and northward flowing water mass respectively mainly antarctic intermediate water and subtropical underwater the observed carbonate mounds are concentrated in these moats mound type 1 has an elongated shape parallel to the prevailing bottom current direction a gently inclined flank facing the water flow and a steep flank in its current shadow its upstream flank is covered by a thin sediment wedge whereas the lee side is marked by a parabolic scour type 1 occurs at both bank margins but mainly off great bahama bank consisting of cold water coral rubble floating in a sediment matrix and is thus interpreted as cold water coral mound by contrast type 2 mounds are restricted to the cay sal margin and have a predominately conical outline bottom samples including living sessile crinoids show that its surface must be lithified and colonized by macroepibenthos except corals the mounds are situated in pockmark like depressions that are underlain by fluid escape structures like pipes and chimneys these fluid pathways are generated by a network of fractures mound type 2 is probably formed by abiotic carbonate precipitation however a chemoherm nature cannot be ruled out mound type 3 has a conical to polygonal shape and occurs off cay sal bank and great bahama bank it is surrounded by a scour which is elongated in downcurrent and crescent in upcurrent direction a sediment bulge formed at its front this type is consistent with blocks and boulders colonized by macroepibenthos and related to gravity controlled mass movements at the steep bank slopes principally two habitats can be distinguished the great bahama bank periplatform deep water province dominated by mound type 1 and the cay sal bank slope to basin province occupied by mound type 2 that is associated with pockmark like structures mound type 3 occurs in both habitats physical water mass properties for the existence of cold water corals are limited to a depth range of ca 430 to 685 m with seawater densities of 26 93 to 27 29 kg m and temperatures below 13 c their dominance off great bahama bank might be addressed to a more effective food supply induced by local downwelling

mineralogy and grain size variations along two carbonate margin to basin transects pedro bank northern nicaragua rise abstract the analysis of nine periplatform cores in the surrounding of the pedro bank carbonate platform showed the presence of characteristic depositional environments during the last 300 ky this subdivision is based on mineralogical and grain size variations in space and time along the leeward downcurrent transect the fine sediment fraction 40 km aragonite is still the most abundant mineral but the percentage decreases while the pelagic carbonate mineral content lmc increases within the subordinate coarse fraction classes 63 m the very fine sand fraction dominates at proximal sites 20 km show a more bimodal distribution pattern in the coarse grain sizes with maximum percentages within the very fine and medium sand fraction indicating a mixed neritic pelagic signal during glacial lowstands in sea level a twofold division in the spatial distribution of the periplatform sediments is evident a proximal environment 28 km showing a strong dominance of the fine fraction 90 the increased coarse fraction percentage during glacials at proximal sites results from various interacting processes 1 lower input of fine neritic sediments 2 increased current winnowing and 3 redepositional processes at the upper slope during lowered sea level and the export of this material to proximal basinal sites at upcurrent sites the mineralogy displays a similar spatial evolution as seen along the downcurrent margin but with overall reduced percentages this is the result of the lower export potential of the platform against the main direction of the caribbean current the most important factor for neritic sediment dispersal in the study area the coarse fraction content is slightly higher during interglacials compared to the downcurrent margin during glacials a similar reduction in the percentage of the coarse fraction is evident in a spatial context this also substantiates the reduced sediment export and redeposition potential at the upcurrent margin