a major circulation anomaly in the western bering sea the alaskan stream ceased to flow northward into the western bering sea starting in summer 1990 this unexpected lack of inflow caused by a southward shift in the path of the alaskan stream persisted through at least fall 1991 if the anomalous flow continues substantial changes in the physical environment will occur possibly leading to impacts on the rich fisheries stocks in the region

characteristics of turbulent boundary layers over a rough bed under saw tooth waves and its application to sediment transport article i nfo a large number of studies have been done dealing with sinusoidal wave boundary layers in the past however ocean waves often have a strong asymmetric shape especially in shallow water and net of sediment movement occurs it is envisaged that bottom shear stress and sediment transport behaviors influenced by the effect of asymmetry are different from those in sinusoidal waves characteristics of the turbulent boundary layer under breaking waves saw tooth are investigated and described through both laboratory and numerical experiments a new calculation method for bottom shear stress based on velocity and acceleration terms theoretical phase difference and the acceleration coefficient ac expressing the wave skew ness effect for saw tooth waves is proposed the acceleration coefficient was determined empirically from both experimental and baseline k model results the new calculation has shown better agreement with the experimental data along a wave cycle for all saw tooth wave cases compared by other existing methods it was further applied into sediment transport rate calculation induced by skew waves sediment transport rate was formulated by using the existing sheet flow sediment transport rate data under skew waves by watanabe and sato watanabe a and sato s 2004 a sheet flow transport rate formula for asymmetric forward leaning waves and currents proc of 29th icce asce pp 1703 1714 moreover the characteristics of the net sediment transport were also examined and a good agreement between the proposed method and experimental data has been found

production of mud grade carbonates by marine fish crystalline products and their sedimentary significance recent work has established that marine teleost bony fish represent a prolific source of mud grade mainly high mg calcite carbonate sediment by means of primary precipitation within the intestine previously documented crystalline products display a diverse array of morphologies many unique in shallow tropical marine settings and have a wide range of magnesium contents from 18 to 39 mol mgco3 this study utilizes scanning electron microscopy energy dispersive x ray spectroscopy x ray diffraction and liquid ion chromatography to provide a more extensive and expansive morphological mineralogical and chemical characterization of the crystalline forms produced by a wider range of piscine functional groups covering 21 different fish species common in the bahamas several crystal morphologies not previously described in fish derived carbonates are documented and chemical composition is found to be more variable than previously reported in addition to high mg calcites with 18 mol mgco3 high mg calcites with lower mgco3 contents and low mg calcites are identified from the expanded species range mgco3 content in fish derived carbonates ranges from ca 0 5 to 40 mol and particle length is in the range 0 1 to 50 m typically 2 m for individual crystals amorphous mg carbonates with detectable caco3 of 2 mol are also found to varying extent in the precipitates of many species dominant mineralogy and mgco3 content varies with producing species and crystal morphology itself a species dependent variable given the very small grain size and often high mgco3 contents of these carbonates interesting questions arise about their preservation potential thus the extent to which carbonates produced by different species may follow different post excretion preservation pathways is considered

the shedding of an anticyclonic eddy from the alaskan stream as observed by the geosat altimeter the evolution of a meander into an anticyclonic eddy which separates from the alaskan stream in the vicinity of the central aleutian islands is observed in two years of sea surface height anomalies computed from geosat exact repeat mission altimeter data the trajectory of the center of mass is estimated using a modified perpendicular bisector method eddy separation is inferred to occur where the trajectory makes a distinct turn to the southwest the observed region of meander growth and eddy separation agrees with that predicted by theory the evolution of meander eddy height and radius is estimated from least squares fits of the data to an axially symmetric gaussian profile the heights and radii are used to calculate the strength vorticity and energetics of the meander eddy ekman dynamics are assumed to govern the eddy decay spin down times based on vorticity are much longer than those based on energetics this is consistent with an eddy s ability to maintain its integrity as it decays representative height diameter and velocity scales of the eddy are characteristic of rings spawned by other current systems assuming a ring structure for this eddy the estimated ring volume represents a 21 transport anomaly referenced to the mean annual transport into the bering sea

laboratory observation of boundary layer flow under spilling breakers in surf zone using particle image velocimetry abstract a boundary layer flow under spilling breakers in a laboratory surf zone with a smooth bottom is investigated using a high resolution particle image velocimetry piv technique by cross correlating the images oscillatory velocity profiles within a viscous boundary layer of o 1 mm in thickness are resolved over ten points using piv measurements taken for an earlier study and the present study flow properties in the wave bottom boundary layer wbbl over the laboratory surf zone are obtained including the mean velocities turbulence intensity reynolds stresses and intermittency of coherent events the data are then used to estimate the boundary layer thickness phase variation and bottom shear stress it is found that while the time averaged mass transport inside the wbbl is onshore in the outer surf zone it changes to offshore in the inner surf zone the zero eulerian mass transport occurs at h hb 0 92 in the outer surf zone the maximum overshoot of the streamwise velocity and boundary layer thickness are not constant across the surf zone the bottom shear stress is mainly contributed by the viscous stress through mean velocity gradient while the reynolds stress is small and negligible the turbulence level is higher in the inner surf zone than that in the outer surf zone although only a slight increase of turbulent intensity is observed inside the wbbl from the outer surf zone to the inner surf zone the variation of phase inside and outside the wbbl was examined through the spatial velocity distribution it is found the phase lead is not constant and its value is significantly smaller than previous thought by analyzing instantaneous velocity and vorticity fields a remarkable number of intermittent turbulent eddies are observed to penetrate into the wbbl in the inner surf zone the size of the observed large eddies is about 0 11 to 0 16 times the local water depth its energy spectra follow the 5 3 slope in the inertial subrange and decay exponentially in the dissipation subrange

multi year meanders and eddies in the alaskan stream as observed by topex poseidon altimeter the birth life and decay of long lived anticyclonic eddies or meanders in the alaskan stream are observed from topex poseidon t p satellite their surface height anomalies approach 72 cm average diameter is about 160km and they live for 1 to 3 years propagating along the stream with mean speed of 2 5 km d 1 of the six observed the last three were formed after the first t p observations in september 1992 of these two evolved from eddies near alaskan panhandle in winter drifting across the northern gulf of alaska before entering the alaskan stream while another formed in the stream west of shelikof strait

bed shear stress under skewed and asymmetric oscillatory flows abstract we present a new formulation to predict the bed shear stress under skewed asymmetric oscillatory flows with or without a co linear mean current extending the work of nielsen 1992 the nonlinearity of the oscillatory flow is incorporated through the use of two parameters the index of skewness or nonlinearity and the waveform parameter the new formulation is tested against the bed shear stress estimated from the log fit and momentum integral methods using oscillatory data from oscillating water tunnel experiments the new formulation and the momentum integral method agree well but differ from those with the log fit method possibly because both methodologies lead to different results for the phase lead between the bed shear stress and the free stream velocity the new bed shear stress formulation is incorporated in a quasi steady bedload formula and accurately reproduces net transport rates under non linear nonbreaking waves with and without an opposing current

seabed shear stress and bedload transport due to asymmetric and skewed waves abstract a simple conceptual formulation to compute seabed shear stress due to asymmetric and skewed waves is presented this formulation generalizes the sinusoidal wave case and uses a variable friction factor to describe the physics of the boundary layer and to parameterize the effects of wave shape predictions of bed shear stresses agree with numerical computations using a standard boundary layer model with a k e turbulence closure the bed shear stress formulation is combined with a meyer peter and muller type formula to predict sheet flow bedload transport under asymmetric and skewed waves for a horizontal or sloping bed the predictions agree with oscillatory water tunnel measurements from the literature

sediment generation by halimeda on atoll interior coral reefs of the southern maldives a census based approach for estimating carbonate production by calcareous green algae abstract methods for quantifying rates and size fractions of carbonate sand production on reefs remain limited despite the urgent need for such data to support assessments of reef island and tropical beach dominated shoreline resilience here we present a census based approach that supports estimates of sediment generation by the calcareous green alga halimeda spp which is an often conspicuous reef and lagoon substrate coloniser based on data from kandahalagala south huvadhoo atoll southern maldives we present carbonate sediment production data for the two dominant halimeda spp halimeda macrophysa and halimeda micronesica that occur on the reef flat and reef slope habitats whilst total mean production rates by halimeda spp are similar in both habitats reef flat average 67 49 g caco 3 m 2 yr 1 reef slope 70 89 g individual species contributions differ markedly h micronesica dominates on the reef flat annual mean 41 91 g caco 3 m 2 yr 1 compared to 25 08 g by h macrophysa whilst production is dominated by h macrophysa on the reef slope h macrophysa 40 49 g h micronesica 29 01 g caco 3 m 2 yr 1 in terms of sediment generation we show that these species also contribute very differently to the sediment reservoir whilst the sedimentary breakdown products from h micronesica are somewhat bimodal 17 is in the medium to very coarse sand fraction and 76 in the silt and clay fraction almost all 90 of the segments produced by h macrophysa rapidly degrade to silt and clay sized sediment based on our census data this suggests that halimeda spp will contribute only between 7 and 9 g m 2 yr 1 of sand grade sediment on the reef flat and shallow slope habitats but 55 60 g m 2 yr 1 of mud grade sediment scaled to the total area of combined reef habitat around kandahalagala 130 583 m 2 this equates to halimeda spp producing 2192 kg of sand grade sediment but 15 181 kg of mud grade sediment per year however sediment compositional data suggests that halimeda sp are actually a very minor constituent of reef and islands sediments especially in the fine sediment fractions this 1 suggests that much of the predominantly finer grained sediment generated by halimeda has little actual relevance to the later stages of reef island development and 2 highlights the potential for marked discrepancies in terms of sediment generating reef species abundance and resultant sediment generation rates especially in terms of the types and sizes of sediment that are appropriate to supply adjacent beaches and islands

practical sand transport formula for non breaking waves and currents many existing practical sand transport formulae for the coastal marine environment are restricted to a limited range of hydrodynamic and sand conditions this paper presents a new practical formula for net sand transport induced by non breaking waves and currents the formula is especially developed for cross shore sand transport under wave dominated conditions and is based on the semi unsteady half wave cycle concept with bed shear stress as the main forcing parameter unsteady phase lag effects between velocities and concentrations which are especially important for rippled bed and fine sand sheet flow conditions are accounted for through parameterisations recently recognised effects on the net transport rate related to flow acceleration skewness and progressive surface waves are also included to account for the latter the formula includes the effects of boundary layer streaming and advection effects which occur under real waves but not in oscillatory tunnel flows the formula is developed using a database of 226 net transport rate measurements from large scale oscillatory flow tunnels and a large wave flume covering a wide range of full scale flow conditions and uniform and graded sands with median diameter ranging from 0 13 mm to 0 54 mm good overall agreement is obtained between observed and predicted net transport rates with 78 of the predictions falling within a factor 2 of the measurements for several distinctly different conditions the behaviour of the net transport with increasing flow strength agrees well with observations indicating that the most important transport processes in both the rippled bed and sheet flow regime are well captured by the formula however for some flow conditions good quantitative agreement could only be obtained by introducing separate calibration parameters the new formula has been validated against independent net transport rate data for oscillatory flow conditions and steady flow conditions

laboratory study of solitary wave transformation over bed form roughness on fringing reefs abstract this paper presents the formulation and implementation of a series of two dimensional flume experiments to investigate effects of bed form roughness on coastal wave processes the experiments were carried out on a fringing reef model in a 104 m long and 4 6 m high flume at oregon state university the reef model has a 1 12 face slope and a long flat section for examination of wave shoaling and breaking as well as bore formation and propagation the model is 2 36 m tall and the water depth ranges from 2 36 to 2 66 m to produce dry and wet reef conditions the bed form roughness is modeled by timber beams placed across the flume in four configurations by varying the height from 0 038 to 0 076 m and the spacing from 0 388 to 0 768 m to provide a range of pitch ratios from 5 to 20 the incident solitary wave height varies from 10 to 50 of the water depth to cover a range of breaking and non breaking conditions a series of wire and sonic gauges measured the wave transformation along the flume and a digital camera recorded images of the breaking waves on a background grid painted on a flume wall the bed forms decrease the effective depth for wave propagation and modify the structure of the free surface flow in comparison to a control experiment with plain concrete surface the solitary wave breaks earlier and dissipates more energy on the reef slope the subsequent bore slows down with undulation over the shallow reef flat but speeds up for more energetic flows in deeper water

effects of wave shape on sheet flow sediment transport 1 a two phase model is implemented to study the effects of wave shape on the transport of coarse grained sediment in the sheet flow regime the model is based on balance equations for the average mass momentum and fluctuation energy for both the fluid and sediment phases model simulations indicate that the responses of the sheet flow such as the velocity profiles the instantaneous bed shear stress the sediment flux and the total amount of the mobilized sediment cannot be fully parameterized by quasi steady free stream velocity and may be correlated with the magnitude of local horizontal pressure gradient or free stream acceleration a net sediment flux in the direction of wave advance is obtained for both skewed and saw tooth wave shapes typical of shoaled and breaking waves the model further suggests that at critical values of the horizontal pressure gradient there is a failure event within the bed that mobilizes more sediment into the mobile sheet and enhances the sediment flux preliminary attempts to parameterize the total bed shear stress and the total sediment flux appear promising

effects of mesoscale eddies on the flow of the alaskan stream 1 using a high resolution pan arctic ice ocean model forced with realistic atmospheric data we examine the mean transport and temporal and spatial variability within the alaskan stream model results are analyzed and compared with observations including satellite altimetry and ctd measurements the mean net transport of the alaskan stream is found to be between 34 and 44 sv intensifying downstream mesoscale eddies are found to periodically move along the path of the alaskan stream and alter the mean position of the typically westward flowing current however the strength of the current is not reduced as an anticyclonic eddy passes a point along the path instead there appears to be an offshore or southward shift in the current velocity core stationary measurement instruments may not be able to detect this shift in position over the slope if their southernmost location does not coincide with the current shift due to an eddy this may result in recording of a weakened or sometimes reversed flow finally we examine and demonstrate that modeled eddies within the alaskan stream have dominant effect on northward transport and variability through the eastern and central aleutian island passes

boundary layer hydrodynamics and bedload sediment transport in oscillating water tunnels oscillating water tunnels are experimental facilities commonly used in coastal engineering research they are intended to reproduce near bed hydrodynamic and sediment transport phenomena at a realistic scale in an oscillating water tunnel a piston generates an oscillatory motion that propagates almost instantaneously to the whole tunnel consequently flow is uniform along the tunnel unlike the propagating wave motion in the sea or in a wave flume this results in subtle differences between the boundary layer hydrodynamics of an oscillating water tunnel and of a propagating wave which may have a significant effect in the resulting sediment transport in this paper we present a zeroth order analytical model of the turbulent boundary layer hydrodynamics in an oscillating water tunnel by using a time varying eddy viscosity and by accounting for the constraints arising from the tunnel s geometry the model predicts the oscillating water tunnel hydrodynamics and yields analytical expressions to compute bed shear stresses for asymmetric and skewed waves both in the absence or presence of an imposed current these expressions are applied to successfully quantify bedload sediment transport in oscillating water tunnel experiments

on the structure paths and fluxes associated with agulhas rings in january 1993 two agulhas rings were sampled in the eastern south atlantic during the world ocean circulation experiment one time hydrographic section a11 the first of these ring 1 was sampled at 36 s 4 e in the subtropical frontal zone and was smaller and less energetic than other more typical agulhas rings owing partly to its interactions with the north subtropical front the other ring 2 was sampled at 33 s 10 e in the subtropics this ring was average in size and reasonably representative of the rings observed in the southeast atlantic during the early 1990s the path of the rings is found to be dominated by advection in the mean flow rather than self induced velocities of eddies under the effect we observe significant differences in reduced gravity and available heat and salt anomalies in the rings from these we infer temporal variability in the stratification of rings upon their formation at the agulhas retroflection this temporal variability in the structure of rings will affect the fluxes associated with them data collected within ring 2 show that neglecting consideration of the water beneath the 10 c isotherm underestimates the volume flux by half and the potential temperature and salinity flux by in excess of one third and one half respectively using a base of the 3 5 c isotherm and including the high salinity intermediate water from the indian ocean is found to be more appropriate with these conditions six agulhas rings per year entering the subtropical south atlantic would equate to a volume flux of 9 sv and an absolute potential temperature and salinity flux of 84 sv c and 322 sv psu 1 sv psu 106 kg s 1 the significant flux of intermediate water from the indian ocean may be as important in the return path of the thermohaline circulation as the intermediate water that enters the south atlantic through drake passage further the water associated with agulhas rings and cooler than 10 c potentially contributes a larger volume flux to the warm water return path than the corresponding surface and upper thermocline water

rapid thermohaline transition in the pacific western subarctic and oyashio fresh core eddies seven years of conductivity temperature depth data enable direct computations of volume transport and a description of the temporal changes of water properties in the western subarctic pacific the cooling of the western subarctic surface layer is shown through the observation of the thermohaline transition which occured in the western subarctic during 1990 1997 its main consequences were changes of the oyashio path and restratification of the western subarctic water the example presented here uses data obtained during the canada russia international north pacific ocean climate study as well as the russian project subarctic to show that a warming and ventilation of the midlayers of the western subarctic 200 1000 dbar occurred because of the influx of warm subtropical waters to the oyashio and sea of okhotsk and to the weak coastal oyashio before the transition this influx appears to have reversed in the early 1990s now subarctic intermediate waters displace the remnants of subtropical waters that penetrated to the sea of okhotsk through the soya strait and create strong stratification in the oyashio area this transition appears to have begun during the reinforcement in the coastal oyashio

surf zone cross shore boundary layer velocity asymmetry and skewness an experimental study on a mobile bed 1 an experimental study on a physical model of a beach in a two dimensional wave flume was designed to investigate velocity nonlinearities in the wave boundary layer the cross shore velocity was measured in the surf zone along a vertical profile every 3mm from free stream elevation down to the still bed level the skewness and the asymmetry of the phase averaged velocity were computed at each elevation observations indicate that the free stream asymmetry transforms into bottom velocity skewness a linear experimental relation between free stream asymmetry to skewness ratio and bottom skewness to free stream skewness ratio is established a theoretical linear relationship is discussed which predicts the phase lead of the bottom velocity this phase lead is also determined by fourier analyzing the velocity time series the first two fourier components yield the same phase lead at the bed that is found to be about 30 and nearly constant over all the experiments made

satellite and hydrographic observations of the bering sea green belt abstract green belt is the aptly named region of high productivity occurring principally along and above the shelf slope boundary in the bering sea topex altimeter measurements of sea surface topography seawifs imagery of chlorophyll a concentration and shipboard measurements of salinity and fluorescence are used to describe the surface structure of the green belt and its relationship to the bering slope current eddy field during the 2000 2001 and 2002 spring blooms during spring 2000 high surface chlorophyll a concentrations 10 mg m 3 were observed within a 200 km wide band adjacent to and seaward of the shelf break in the northwest bering sea this high concentration chlorophyll band was associated with an anticyclonic eddy group that propagated along isobaths above the continental slope and entrained chlorophyll from the shelf slope front during spring 2001 anticyclonic eddies in the northwest bering sea had propagated off slope prior to the onset of the spring bloom and were too far from the shelf slope front to entrain frontal chlorophyll during the bloom a second chlorophyll front associated with the leading edge of the off slope eddies was observed between these two fronts was a region of relatively low chlorophyll a concentration 1 mg m 3 the eddy field during the 2002 spring bloom was observed to propagate northwestward adjacent to the shelf break and entrain chlorophyll from the shelf slope region in a manner similar to what was observed during the 2000 spring bloom these observations suggest that eddies are important if not the principal agents that cause variability in the distribution of chlorophyll during the spring bloom in the central bering sea

a comparative study of modern carbonate mud in reefs and carbonate platforms mostly biogenic some precipitated abstract carbonate mud from reefs and carbonate platforms in six locations of the atlantic indian and pacific oceans belize bahamas florida the maldives french polynesia great barrier reef was systematically and quantitatively analyzed with regard to texture composition mineralogy and geochemistry mud composition shows considerable variability however the data supports the contention that these muds are largely derived from the breakdown of skeletal grains and codiacean algae only mud from the bahamas and northern belize areas which are characterized by common whitings is interpreted to be mainly inorganically precipitated three grain size fractions 63 20 m 20 4 m

boundary layer approach in the modeling of breaking solitary wave runup abstract the boundary layer is very important in the relation between wave motion and bed stress such as sediment transport it is a known fact that bed stress behavior is highly influenced by the boundary layer beneath the waves specifically the boundary layer underneath wave runup is difficult to assess and thus it has not yet been widely discussed although its importance is significant in this study the shallow water equation swe prediction of wave motion is improved by being coupled with the k model as opposed to the conventional empirical method to approximate bed stress subsequently the first order center scheme and monotonic upstream scheme of conservation laws force muscl which is a finite volume shock capturing scheme is applied to extend the swe range for breaking wave simulation the proposed simultaneous coupling method scm assumes the depth averaged velocity from the swe is equivalent to free stream velocity in turn free stream velocity is used to calculate a pressure gradient which is then used by the k model to approximate bed stress finally this approximation is applied to the momentum equation in the swe two experimental cases will be used to verify the scm by comparing runup height surface fluctuation bed stress and turbulent intensity values the scm shows good comparison to experimental data for all before mentioned parameters further analysis shows that the wave reynolds number increases as the wave propagates and that the turbulence behavior in the boundary layer gradually changes such as the increase of turbulent intensity

validation of a new generation system for bottom boundary layer beneath solitary wave abstract understanding of sea bottom boundary layer characteristics especially bottom shear stress acting on the sea bed is an important step needed in sediment transport modeling for practical application purposes in the present study a new generation system for bottom boundary layer under solitary wave is proposed applicability of this system is examined by comparing measured and numerical solution velocities moreover transitional behavior from laminar to turbulence was investigated it is concluded that the critical reynolds number in the experiments shows good agreement with dns result of vittori and blondeaux 2008 and laboratory data of sumer et al 2010 indicating validity of the generation system since the present generation system enables continuous measurement to obtain ensemble averaged quantities it can be effectively utilized for future experimental studies on solitary wave boundary layers including sediment transport experiments with movable bed

variability of the kuroshio extension jet recirculation gyre and mesoscale eddies on decadal time scales abstract twelve years of sea surface height ssh data from multiple satellite altimeters are used to investigate the low frequency changes and the interconnections of the kuroshio extension ke jet its southern recirculation gyre and their mesoscale eddy field the dominant signal is characterized by the steady weakening of the ke jet recirculation gyre from 1993 to 1996 followed by a gradual strengthening after 1997 during the weakening period of 1993 96 the ke path migrated southward in general and this path migration reversed in direction during the strengthening period of the ke jet and recirculation gyre after 1997 by hindcasting the ssh signals using linear vorticity dynamics it was found that weakening strengthening in the ke jet and recirculation gyre is consistent with westward propagation of negative positive ssh anomalies generating in the eastern north pacific and strengthening during their westward propagation when the ke jet and recirculation gyre were in a weak mode during 19

reef fish carbonate production assessments highlight regional variation in sedimentary significance recent studies show that all marine bony fish produce mud sized 63 mu m carbonate at rates relevant to carbonate sediment budgets thus adding to the debate about the often enigmatic origins of fine grained marine carbonates however existing production data are geographically and taxonomically limited and because different fish families are now known to produce different carbonate polymorphsan issue relevant to predicting their preservation potential these limitations represent an important knowledge gap here we present new data from sites in the western pacific ocean based on an analysis of 45 fish species our data show that previously reported production outputs in terms of rates and family specific mineralogies are applicable across different biogeographic regions on this basis we model carbonate production for nine coral reef systems around australia with production rates averaging 2 1 9 6 g m 2 yr 1 and up to 105 g m 2 yr 1 at discrete sites with high fish biomass with projected production rates on lower latitude reefs up to two fold higher these outputs indicate that carbonate production rates by fish can be comparable with other fine grained carbonate producing taxa such as codiacean algae however carbonates produced by australian reef fish assemblages are dominated by a highly unstable amorphous polymorph a marked contrast to caribbean assemblages in which mg calcite dominates these findings highlight important regional differences in the sedimentary relevance and preservation potential of fish carbonates as a function of historical biogeographic processes that have shaped the world s marine fish faunas

measurements of sheet flow transport in acceleration skewed oscillatory flow and comparison with practical formulations near bed oscillatory flows with acceleration skewness are characteristic of steep and breaking waves in shallow water in order to isolate the effects of acceleration skewness on sheet flow sand transport new experiments are carried out in the aberdeen oscillatory flow tunnel the experiments have produced a dataset of net transport rates for full scale oscillatory flows with varying degrees of acceleration skewness and three sand sizes the new data confirm previous research that net transport in acceleration skewed flow is non zero is always in the direction of the largest acceleration and increases with increasing acceleration skewness large transport rates for the fine sand conditions suggest that phase lag effects play an important role in augmenting positive net transport a comparison of the new experimental data with a number of practical sand transport formulations that incorporate acceleration skewness shows that none of the formulations performs well in predicting the measured net transport rates for both the fine and the coarser sands the new experimental data can be used to further develop practical sand transport formulations to better account for acceleration skewness

the shedding of mesoscale anticyclonic eddies from the alaskan stream and westward transport of warm water abstract the south flowing waters of the kamchatka and oyashio currents and west flowing waters of the alaskan stream are key components of the western sub arctic pacific circulation we use ctd data argo buoys woce surface drifters and satellite derived sea level observations to investigate the structure and interannual changes in this system that arise from interactions among anticyclonic eddies and the mean flow variability in the temperature of the upstream oyashio and kamchatka currents is evident by warming in mesothermal layer in 1994 2005 compared to 1990 1991 a major fraction of the water in these currents is derived directly from the alaskan stream the stream also sheds large anticyclonic aleutian eddies averaging approximately 300 km in diameter with a volume transport significant in comparison with that of the kamchatka current itself these eddies enclose pools of relatively warm and saline water whose temperature is typically 4 c warmer and salinity is 0 4 greater than that of cold core kamchatka eddies in the same density range aleutian eddies drift at approximately 1 2 km d 1 and retain their distinctive warm and salty characteristics for at least 2 years selected westward pathways during 1990 2004 are identified if the shorter northern route is followed aleutian eddies remain close to the stream and persist sufficiently long to carry warm and saline water directly to the kamchatka current this was observed during 1994 1997 with substantial warming of the waters in the kamchatka current and upstream oyashio if the eddies take a more southern route they detach from the stream but can still contribute significant quantities of warm and saline water to the upstream oyashio as in 2004 2005 however the eddies following this southern route may dissipate before reaching the western boundary current region

recent variability in the pacific western subarctic boundary currents and sea of okhotsk abstract the objective of this research is to describe physical processes which are the cause of the recent variability of the pacific western subarctic waters rapid thermohaline changes have occurred within the oyashio and kamchatka current during the last decade this variability has included a warming of the kamchatka current warm intermediate layer but a cooling and freshening of the upper layer in the oyashio and sea of okhotsk the example presented here uses data obtained during the canada russia inpoc and woce projects as well as the new russian studies with high resolution station grid the possible physical mechanism that generated the upper layer freshening during the thermohaline transition is examined major components of the fresh water budget of the okhotsk sea are considered in order to describe the dramatic changes in salinity which have recently occurred in the pacific subarctic significant changes in precipitation and other fresh water inputs are demonstrated it is suggested that upper layer of the oyashio and kamchatka current became cooler and fresher because of the export of cold fresher waters from the bering and okhotsk seas these waters from the marginal seas have cooled the bottom of the halocline reducing evaporation and acting as a feedback that has kept the upper layer of the western subarctic boundary currents fresh it is also shown that the outflow of the cold sea of okhotsk water has changed its path during this recent thermohaline transition

mesoscale eddies dominate surface phytoplankton in northern gulf of alaska abstract the hnlc waters of the gulf of alaska normally receive too little iron for primary productivity to draw down silicate and nitrate in surface waters even in spring and summer our observations of chlorophyll sensed by seawifs north of 54 n in pelagic waters 500 m depth of the gulf found that on average more than half of all surface chlorophyll was inside the 4 cm contours of anticyclonic mesoscale eddies the ratio approaches 80 in spring months yet these contours enclosed only 10 of the total surface area of pelagic waters in the gulf therefore eddies dominate the chlorophyll and phytoplankton distribution in surface pelagic waters we outline several eddy processes that enhance primary productivity eddies near the continental margin entrain nutrient and fe rich and chlorophyll rich coastal waters into their outer rings advecting these waters into the basin interior to directly increase phytoplankton populations there in addition eddies carry excess nutrients and iron in their core waters into pelagic regions as they propagate away from the continental margin as these anticyclonic eddies decay their depressed isopycnals relax upward injecting nutrients up toward the surface layer we propose that this transport brings iron and macro nutrients toward the surface mixed layer where they are available for wind forced mixing to bring them to surface these mesoscale eddies decay slowly but steadily perhaps providing a relatively regular upward supply of macro nutrients and iron toward euphotic layers they might behave as isolated oases of enhanced marine productivity in an otherwise iron poor basin we note that much of this productivity might be near or just below the base of the surface mixed layer and therefore poorly sampled by colour sensing satellites it is possible then that eddies enrich phytoplankton populations to a greater extent than noted from satellite surface observations only

benthic carbonate factories of the phanerozoic marine carbonate precipitation occurs in three basic modes abiotic or quasi abiotic biotically induced and biotically controlled on a geologic scale these precipitation modes combine to form three carbonate production systems or factories in the benthic environment 1 tropical shallow water factory dominated by biotically controlled mainly photo autotrophic and abiotic precipitates 2 cool water factory dominated by biotically controlled mainly heterotrophic precipitates and 3 mud mound factory dominated by biotically induced mainly microbial and abiotic precipitates sediment accumulations of the factories differ in composition geometry and facies patterns and some of these differences appear prominently in seismic data thus facilitating subsurface prediction the characteristic accumulation of the tropical factory is the flat topped often reef rimmed platform in cool water systems reefs in high energy settings are scarce and hydrodynamic influence dominates producing seaward sloping shelves and deep water sediment drifts often armored by skeletal framework the typical accumulation of the mud mound factory is groups of mounds in deeper water where the mud mound factory expands into shallow water it forms rimmed platforms similar to the tropical factory the tropical factory is most productive the mud mound factory reaches 80 90 and the cool water factory 20 30 of the tropical growth rate the three factories represent end members connected by transitions in space transitions in time are linked to biotic evolution

size fraction analysis of fish derived carbonates in shallow sub tropical marine environments and a potentially unrecognised origin for peloidal carbonates abstract marine bony fish are now known as primary producers of calcium carbonate furthermore within the shallow sub tropical platform settings of the bahamas this production process has been shown to occur at rates relevant to carbonate sediment production budgets fish excrete these carbonates as loosely aggregated pellets which post excretion exhibit a range of distinctive crystal morphologies and have mineralogies ranging from low 0 4 mol mgco 3 to high 4 40 mol mgco 3 mg calcites aragonite and amorphous carbonate phases here we provide the first quantitative assessment of the size fractions of the carbonates produced by a range of tropical fish species and document the extent of post excretion carbonate pellet break down under a range of physical agitation conditions specifically we document the morphologies and size fractions of i intact pellets at the point of excretion ii intact pellets after agitation in seawater and iii the particles released from pellets post disaggregation results indicate that fish derived pellets initially fall within the very fine to very coarse sand fractions exposure to conditions of moderate seawater agitation for 30 days results in significant pellet diminution 66 of initial pellet mass being released as individual particles whilst 34 is retained as partially intact pellets that are smaller fine sand grade and more rounded than initial pellets in contrast pellets exposed to very gently agitated conditions for up to 200 days show little change where pellet disaggregation does occur particles are commonly released as individual clay and silt grade crystals however some morphotypes e g polycrystalline spheres can be intergrown and are released as strongly cohesive particle clusters falling within the coarse silt to fine sand fractions only very vigorous agitation may disaggregate such particles resulting in the release of their component clay grade crystals we conclude that fish derived carbonates may thus contribute not only to the mud fraction of marine carbonates but also to the fine sand fraction as intergrown particles and to the fine to coarse sand fractions as intact and partially intact pellets these experimental data indicate that hydrodynamic regimes local to sites of excretion will influence the generation of carbonates with different size fraction ranges rapid pellet disaggregation is more likely in high energy settings hypothesised to result in redistribution of liberated mud grade particles to lower energy platform top settings and or off platform in contrast pellets excreted in lower energy settings are more likely to be preserved intact and are thus proposed as a previously unrecognised source of pelletal and peloidal carbonate sediments

satellite and hydrographic observations of eddy induced shelf slope exchange in the northwestern gulf of alaska 1 satellite and hydrographic observations of oceanographic conditions in the northwestern gulf of alaska indicate that anticyclonic eddies propagating adjacent to the continental shelf alter the structure of the shelf break front and in doing so influence the shelf slope exchange of biota and water mass properties eddies typically form in the northern gulf of alaska during fall and winter and propagate southwestward within an 200 km wide corridor along and above the continental slope eddy activity within this corridor diminishes in the downstream direction the trajectories of faster propagating 4 km day eddies tend to lie closer to the shelf break than do the trajectories of slower propagating 1 5 km day eddies the interaction between azimuthal eddy currents and the shelf break frontal jet 1 establishes an upwelling zone associated with the leading flank of the eddy that strengthens cross slope gradients 2 weakens cross slope gradients and promotes shelf slope exchange where the eddy is adjacent to the shelf and 3 reestablishes a weak upwelling zone associated with the trailing flank of the eddy

anticyclonic eddies in the alaskan stream abstract anticyclonic eddies propagating southwestward in the alaskan stream as were investigated through analysis of altimetry data from satellite observations during 1992 2006 and hydrographic data from profiling float observations during 2001 06 fifteen long lived eddies were identified and categorized based on their area of first appearance three eddies were present at the beginning of the satellite observations another three formed in the eastern gulf of alaska off sitka alaska and four were first detected at the head of the gulf of alaska near yakutat alaska the other five eddies formed along the as between 157 and 169 w and were named as eddies while the eddies that formed in the gulf of alaska mainly decayed before exiting the gulf of alaska the as eddies mostly crossed the 180 meridian and reached the western subarctic gyre four of five as eddies formed under negative or weakly positive wind stress curls which possibly caused as separation from the coast comparison of eddy propag

shear stress and sediment transport calculations for swash zone modelling it is shown that the observed difference in sediment transporting efficiency by the swash uprush compared with the downrush could be mainly due to greater bed shear stress for a given velocity in the more abruptly accelerated uprush the bed shear stress generated by an arbitrary free stream velocity time series is modelled in terms of usual wave boundary layer models plus a phase lead phi tau of the bed shear stress compared with the free stream velocity at the peak frequency with this approach the total transport amounts in uprush and downrush can be modelled satisfactorily with the same sediment transport formula without the need for different uprush and downrush coefficients while the adaptation of sediment transport formulae from steady flow can thus lead to the right total amounts of sediment moved by this method the timing of the instantaneous sediment transport rates are probably not accurately modelled due to the highly unsteady nature of the swash and the presence of pre suspended sediment in the uprush nevertheless the proposed method is a useful intermediate step before we have a complete understanding of sediment transport under very rapid accelerations and of the relative contribution of pre suspended sediment to the onshore sediment transport in swash zones c 2002 published by elsevier science b v

explicit approximation for velocity and sediment flux above mobile sediment bed beneath current and asymmetric wave abstract an explicit approximation is proposed for velocity distribution and sediment flux above mobile sediment bed beneath current and asymmetric wave the predicted velocity is decomposed into an oscillatory part and a current part such that the interaction between current and asymmetric wave can be performed directly the oscillatory part consists of a free stream velocity and a defect function which includes phase lead mobile sediment bed level and wave boundary layer thickness the oscillatory part is influenced by the current due to the changes of both mobile sediment bed level and wave boundary layer thickness the current part is influenced by a wave eddy viscosity in the wave boundary layer and by an apparent wave roughness of the combined wave current flow outside the wave boundary layer eight free variables are required for the approximation and iterative bottom shear stress and roughness height are applied for the wave boundary layer thickness and mobile sediment bed level the mobile sediment bed level takes account of the effects of phase lag phase shift and residual acceleration and flow asymmetry therefore the mobile bed effect instantaneous velocity net velocity and sediment flux in the wave boundary layer can be reasonably presented by the explicit approximation beneath current and asymmetric wave

the influence of an alaskan stream eddy on flow through amchitka pass flow into the bering sea through amchitka pass in the central aleutian islands is shown to respond to the presence of a large meander eddy in the alaskan stream south of the pass maximum flow into the aleutian basin of the bering sea occurs when the eddy center lies nearest to the axis of amchitka pass a conceptual model of low frequency circulation variability within the bering sea based upon results of empirical orthogonal function analyses of sea surface height anomalies measured by the geosat radar altimeter is presented