tracer transport within abyssal mixing layers abstractmixing layers near sloped topography in the abyss are thought to play a critical role in the global overturning circulation yet the behavior of passive tracers within sloping boundary laye

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

anatomy of turbulence in thermally stratified lakes turbulence within the thermocline of two thermally stratified lakes lake biwa japan and lake kinneret israel was investigated using a portable flux profiler this instrument provided high resolution profiles of temperature conductivity and two components of velocity within a measuring volume of approximately 8 mm 3 each data profile was segmented into statistically stationary segments a range of properties of the turbulence including direct estimates of the vertical mass flux were then calculated for each segment it was found that turbulence in the thermocline was generally patchy but within a patch dissipation levels were relatively high the turbulent motions were found to be fine grained with small thorpe scales and a large skewness of the distribution of the displacement scale this is distinct to that found in the ocean where shear instability produces large overturns the measurement showed that the net vertical mass flux in the thermocline was negligible and less than that predicted by osborn 1980 this is explained by noting that the net buoyancy flux consisted of two opposing parts a down gradient irreversible flux due to turbulent mixing and an up gradient reversible flux due to restratification that often cancel each other within a segment the low measured net buoyancy flux within the interior of the lakes suggested that other processes such as gravitational adjustments and benthic boundary layer processes should be responsible for the basin averaged vertical transport in these lakes

comparison of pelagic and nepheloid layer marine snow implications for carbon cycling abstract marine snow from upper and mid water i e pelagic depths on the california margin is texturally and compositionally different from that traveling in the nepheloid layer transmission electron microscopy shows that pelagic marine snow consists primarily of bioclasts e g diatom frustules foram tests organic matter and microbes these components are entrained as discrete particles or small aggregates 10 m in diameter in a loose network of exocellular muco polysaccharide material clays are infrequent but when present are constituents of comparatively compact organic rich microaggregates microbes are abundant and appear to decrease in number with increasing water depth in contrast marine snow aggregates collected from just above the sea floor in the nepheloid layer are assemblages of clay particles clay flocs and relatively dense clay organic rich microaggregates in an exocellular organic matrix bioclasts and microorganisms occur only rarely the prevalence of clay organic rich aggregates in the nepheloid layer suggests that prior to final deposition and burial marine snow from the pelagic zone is subject to disaggregation and recombination with terrigenous detrital material near or at the sea floor results have significant implications for the accumulation and burial rates of organic carbon on continental margins and the aging and bioavailability of sedimentary organic matter samples examined were collected offshore of northern and central california

constraints on the acquisition of remanent magnetization in fine grained sediments imposed by redeposition experiments the magnetization of sediments is acquired through complex processes involving a large number of physical mineralogical and magnetic parameters despite many attempts the degree to which these processes distort the record of the geomagnetic field as it is archived as a natural remanent magnetization nrm remains poorly documented among many other parameters it is important to evaluate the amount of smoothing inherent to the signal its relation with the field intensity and its variability in the sediment column in order to address these problems we performed new redeposition experiments using carbonate rich ocean drilling program odp site 851 and clay rich odp site 854 sediments we used a dilute solution of gelatin which gels below 20 c thereby allowing mechanical blocking of the magnetic grains we observed two critical results 1 the efficiency of detrital remanent magnetization drm decreases with increasing sediment concentration for a given slurry sediment concentration is defined as c ms ms mh2o where ms and mh2o are the sediment and water mass respectively higher c would then reflect greater compaction lower water content and presumably greater depth in the sediment column this effect reduces drm efficiency nearly to zero for c 50 2 post depositional remanent magnetization pdrm is important for c 50 pdrm is carried by grains covering the entire coercivity spectrum by comparing the mean value of nrm divided by anhysteretic remanent magnetization from the previous magnetostratigraphic study at site 851 with the relevant ratio derived from our redeposition experiments we were able to estimate that pdrm was significant within the depth interval where 44 c 56 if the sediment concentration profile for the uppermost sediment was known at site 851 we could define the transfer function for the deconvolution of the field variations finally the dependence of drm efficiency on c suggests that changes in the thickness of the surface mixed layer would change drm efficiency thus fluctuations in maximum bioturbation depth could possibly cause drm intensity changes regardless of changes in earth s field

comparison of shear measurements and mixing predictions with a direct observation of diapycnal mixing in the atlantic thermocline four sets of velocity and density profiles have been measured with an autonomous profiler during an upper ocean intentional tracer sf6 diapycnal diffusivity measurement the north atlantic tracer release experiment natre the tracer was injected near 310 m depth in the canary basin two profile sets were collected 6 months after tracer release and two were collected i year after release all within the horizontal boundaries of the sf6 patch shear and strain can be combined with turbulent kinetic energy dissipation and diffusivity measurements published elsewhere to test existing expressions for dissipation and diffusivity due to shear induced turbulence these expressions arise from internal wave decay modeling one expression of dissipation parameterized in terms of shear based on stochastic nonlinear internal wave interaction has fared well empirically its extension to estimate diffusivity is evaluated shear variance of the first two data sets was about 1 6 times gm76 and 2 5 to 3 0 times gm76 in the later sets the average parameterized mixing estimate computed using all of the temporally limited shear measurements overestimates annual mean natre diffusivity 1 5 x 10 m 2 s by a factor of 1 2 a modified parameterization gives an underestimate to first order this supports the present understanding of open ocean diffusivity in terms of fine scale shear and internal wave decay that is the slow diapycnal mixing was not a consequence of unusually low shear adjustment of the shear induced mixing models to better fit the data is not warranted because of the lack of direct comparability between the various measurements the expected natural variability of the shear and sampling errors

the role of magnetostatic interactions in sediment suspensions summary the processes that influence a detrital remanent magnetization as well as the physical microscale factors that control formation of a stable post depositional remanent magnetization are still not fully understood previous laboratory studies and statistical numerical approaches have shown the possibility that sediment suspensions can display complex magnetization phenomena such behaviour has been attributed to the effect of magnetostatic interactions in the suspension which could provide one explanation for spurious magnetizations observed in marine sediment cores in laboratory experiments we investigated magnetization decay as a function of time in sediment suspensions produced with varying lithologies and particle concentrations a companion model takes into account the physics of magnetic particle particle interactions brownian motion and hydrodynamic forces to investigate numerically the magnetization behaviour of sediment suspensions when combined the experiments and the numerical models reveal a weak effect of magnetostatic interactions in the natural sediment suspensions which is expressed as an increase in the magnetization decay rate in addition a calculation of effective particle size based on the response of each suspension to brownian motion indicates that the majority of the sedimentary magnetic particles are attached to larger clay particles

salt marsh aggradation in response to late holocene sea level rise at amherst point nova scotia canada a radiocarbon 14c chronology determined for plant macrofossils in exposed salt marsh sediments at amherst point nova scotia canada shows that the edge of the high salt marsh aggraded 7 5 m since 900 bc equivalent to a mean rate of 25 9 cm 100 yr 1 four phases of rapid aggradation 900 600 bc 100 bc ad 200 ad 700 1100 and ad 1600 to present were interspersed with three phases of slower aggradation 600 100 bc ad 200 700 and tentatively ad 1100 1600 the stepped pattern of marsh aggradation probably resulted from eustatic sea level fluctuations superimposed on background signals of crustal subsidence and tidal range expansion because the rate of high salt marsh aggradation lagged or exceeded the rate of higher high water hhw increase at various times the high salt marsh aggradation trend only approximates the trend of hhw increase the eustatic sea level fluctuations are estimated to have a range of at least 0 8 m

boundary mixing in a rotating stratified fluid extension d une experience de laboratoire sur le melange en couche limite dans un fluide stratifie pour inclure les effets de rotation la combinaison du melange vertical a la frontiere et du melange horizontal par des tourbillons d echelle moyenne conduit a l affaiblissement du gradient de densite interieur

comparison of deep ocean finescale shear at two sites along the mid atlantic ridge abstract four drifting floats were used to measure the magnitude of the vertical derivative of horizontal velocity in waters above the rough bathymetry of the mid atlantic ridge this derivative is typically the dominant component of the velocity gradient the shear two floats were at the site of the brazil basin tracer release experiment bbtre in the south atlantic and two were near the site of the guiana abyssal gyre experiment gage in the north atlantic floats operated for 1 year except for one bbtre float which operated for 100 days shear was measured over a vertical span of 9 5 m using drag elements that caused the floats to rotate slowly in response to shear for each float the first second and fourth moments of shear were elevated above levels associated with the garrett munk model internal wave spectrum three of the four floats were tracked as they moved over mountainous terrain allowing shear intensity to be measured as a function of height above the bottom a deep bbtre float showed enhancement of rms shear near the bottom floats at both areas provided measurements at 2000 m above the bottom with differing results the gage site had a lower fourth moment of shear diapycnal diffusivity proxy than the bbtre site however application of normalization factors accounting for differences between the sites in bottom roughness latitude dependent internal wave dynamics and tidal current speeds brings the results into agreement

on a simple empirical parameterization of topography catalyzed diapycnal mixing in the abyssal ocean abstract the global spatial distribution of the turbulent diapycnal diffusivity in the abyssal ocean is reexamined in light of the growing body of microstructure data revealing bottom intensified turbulent mixing in regions of rough topography a direct and nontrivial implication of the observed intensification is that the diapycnal diffusivity k is depth dependent and patchily distributed horizontally across the world s oceans theoretical and observational studies show that bottom intensified mixing is dependent upon a variety of energy sources and processes whose contributions to mixing are sufficiently complex that their physical parameterization is premature only rudimentary parameterizations of tidally induced mixing have been attempted although the tides likely provide no more than half of the mechanical energy available for diapycnal mixing in the abyssal ocean here an empirical and still rudimentary parameterization of the spatially variable mean diffusivity k based on a large collection

compaction and inclination shallowing in deep sea sediments from the pacific ocean progressive downcore shallowing of the remanent inclination has been observed in a 120 m section of marine sediments at deep sea drilling project site 578 in the northwest pacific representing the past 6 5 m y near the top of the section the average inclination corresponds to the expected geocentric axial dipole value of 53 but shallows down section by about 6 to 8 northward translation of the pacific plate accounts for only about a quarter of the inclination shallowing moreover no inclination shallowing was observed at neighboring site 576 which has considerably lower sedimentation rates and the last 5 m y are represented by a 26 m sedimentary section we correlate the inclination shallowing at site 578 with an average decrease in porosity of 3 4 the porosities in the top 26 m at site 576 are slightly higher than at site 578 and show no definite trend downhole we interpret these results to suggest that both the downhole inclination shallowing and decrease of porosity in site 578 are caused by sediment compaction compaction does not play a significant role for the section at site 576 due to its much shorter length

finescale shear at 1660 and 2850 dbar over the mid atlantic ridge in the eastern brazil basin abstract two drifting shearmeter instruments have provided records of the magnitude of shear the magnitude of the vertical derivative of horizontal velocity measured over a 10 m aperture in the vicinity of the brazil basin tracer release experiment the floats drifted at roughly 1660 and 2850 dbar where the buoyancy frequencies were n 1 1 and 0 5 cph respectively two additional floats provided deep trajectories but no shear data the records of hourly mean values of shear magnitude with mean values denoted sh exhibit strong temporal variability with time scales comparable to those of fortnightly tidal modulation the deep record exhibits stronger mean sh near the seafloor than above with the exception of the bin closest to the seafloor sh from neither float correlates strictly with tidal forcing shallow sh varies in apparent response to atmospheric forcing the mean squared shear of the shallow record is 4 times the n dependent value associated with the garrett munk spectral model and that

high resolution record of geomagnetic secular variation from late pleistocene lake lisan sediments paleo dead sea we measured geomagnetic secular variation in lake lisan sediments paleo dead sea more than 1500 oriented samples were collected from a 27 3 m section of alternating aragonite and detritus laminae in the dead sea basin ranging in age from 67 to 32 ka the natural remanent magnetization nrm is carried by titanomagnetite in the detrital laminae whereas the aragonite is diamagnetic the nrm is very stable and was acquired several hundred years after deposition the mean direction of 878 horizons is dd 005o id 45o 95d 1o d 22 we observed three modes of directional geomagnetic variation as a function of and by inference time very rapid inter sample changes slow variation in mean direction and inclination shallowing of about 1o m the overall rate of change in direction is 0 57 0 57o year not significantly different from zero for about 83 of the record the rate of change is less than 1o year and comparable to historical values high rates of change are observed more frequently in the lisan than in historical records and peak rates are up to ten times faster a smoothed curve resulting in a maximum rate of change of 0 66o year and a mean 0 10 0 10o year may be a more realistic representation of the field behavior no reverse nrms were observed but geomagnetic field excursions may be present where the vgps deviate by more than 40o from the geographic north at about 52 and 41 ka the latter may represent the laschamp event 1998 elsevier science b v all rights reserved

the role of boundary mixing in the deep ocean recent laboratory studies demonstrate that mixing at the boundaries of stratified and rotating fluids can be described by a relatively simple parameterization these results are applied to the deep ocean and by using available field observations it is argued that mixing at the boundaries can lead to an apparent diapycnal diffusivity in the interior of the deep ocean whose magnitude has an upper bound of 3 10 5 m2 s 1

effects of ph and salinity on the intensity of magnetization in redeposited sediments abstract the intensity of magnetization in redeposited sediments was measured as a function of salinity and ph of the sediment water mixture the intensity was relatively low at high salinity or low ph under these conditions inter particle bonds are enhanced which lead to the formation of larger flocs ferromagnetic minerals magnetite in our sediment are incorporated in the flocs consisting mainly of non magnetic minerals and orientation along an applied field is resisted by the drag proportional to the third power of the diameter of the floc higher intensity is recorded at lower salinity and higher ph when inter particle forces are weaker and floc sizes are smaller the increase of magnetization as a function of ph stops at a ph of about 5 which is the pzc of the edge of illite the dominant non magnetic mineral in our sediment above this ph both the edge and face of the illite grains are negative and there is net repulsion which retards flocculation the interactions between clay particles therefore have a larger effect on the intensity of magnetization than interactions between magnetite and clay this suggests that magnetite is always included in a clay magnetite domain and this domain is the smallest unit that is reoriented by a magnetic field

radon 222 in the benthic boundary layer a detailed survey of radon 222 and temperature profiles of the benthic boundary layer in the hatteras abyssal plain shows a strong correlation between the structure of both the apparent vertical diffusivities estimated from radon 222 are of the order of 50 cm2 s 1 in the mixed layer and of the order of 1 cm 2 s 1 above it one profile appears to have been taken in a frontal zone where isotherms dip sharply into the sediments this is the only profile where there is significant penetration of radon above the mixed layer several other profiles suggest that the temperature may take longer than several radon half lives to adjust to new mixing and advection regimes in such cases one often sees considerable structure in the radon profile within the region where the potential temperature is well mixed

sediment resuspension and mixing by resonantly generated internal solitary waves the observation of internal solitary waves isws propagating upstream along a strongly stratified bottom layer on the california shelf is reported an increased concentration of particulates in the water column accompanies the passage of these isw packets the estimated local richardson number in the bottom vicinity is around 1 4 and a vertical coefficient of eddy diffusivity of order 1022 m2 s21 is associated with the upstream propagating leading isw the leading isw gave rise to reversed flow in an 8 m layer above the bottom it is argued that the upstream propagating isws were generated by resonant flow over bottom topography internal waves generated in this way seem to be frequent in the record of a month long experiment model results suggest that the isws can carry up to 73 of such generated long wave energy the ocean conditions at the site are similar to those of other coastal sites which suggests that the phenomenon described here may be common

are hydrodynamic shape effects important when modelling the formation of depositional remanent magnetization recent conceptual models have attributed the weak depositional remanent magnetizations observed in natural sediments to flocculation processes in the water column magnetic particles included into flocs have not only to rotate themselves into alignment with the geomagnetic field but also the larger particles to which they are attached making remanence acquisition an inefficient process alignment is hindered further when the magnetization vectors of the particles in any given floc partially cancel reducing the overall magnetic torque existing numerical simulations of flocculation effects on depositional remanence formation have been limited to spherical bodies with translational and rotational motion acting independently of each other in the case of non spherical flocs the translational and rotational motion are coupled and such bodies will describe a complex trajectory through the water column calculations will be presented that show the torque exerted on a non spherical floc by the surrounding water can be orders of magnitude greater than the magnetic torque non spherical flocs will therefore align less efficiently with the geomagnetic field and hydrodynamic effects may play an important role in controlling the magnitude of sedimentary remanence

a study of the bottom boundary layer over the eastward scarp of the bermuda rise velocity and temperature measurements from the bottom boundary layer bbl over the eastward scarp of the bermuda rise in water depth of 4620 m show little variability over an 8 month period the free stream flow 62 m above the bottom was south southeasterly following the isobaths in the region with an average speed of 22 cm s the current vector in the bbl rotated an average of 5 in a counterclockwise sense between 62 and 0 8 m above the bottom the thickness of the bbl was 40 m and the average magnitude of the bottom stress was 0 7 dynes cm2 mean speed profiles height of the bbl and the magnitude of the bottom stress predicted by a model compare favorably with the observations but the model predicts a rotation of the current vector between 62 and 0 8 m more than twice that measured the time dependent nature of the flow field is also reproduced by the model the bermuda rise data and speed profile measurements at the base of the scotian rise show that the m2 clockwise polarized tide is damped more than the mean current as the bottom is approached in the bbl this phenomenon is reproduced by the model and can be explained by differing effective ekman layer thicknesses associated with tidal and steady components of the flow

boundary versus internal diapycnal mixing in stratified natural waters using the fluorescent dye uranin tracer release experiments to study the contribution of bottom boundary mixing to diapycnal transport in stratified natural waters were performed in lake alpnach central switzerland during 1992 1995 a first experiment involved injecting the tracer from a point source into the center of the hypolimnion that part of the lake below the surface mixed layer an in situ fluorometer was then employed to detect the horizontal and vertical spreading of the tracer cloud allowing rates of diapycnal diffusivity to be determined as long as the tracer was confined to the interior water region the diapycnal diffusivity was relatively small however after the tracer cloud had reached the lake boundary the diapycnal diffusivity increased by approximately one order of magnitude in a second experiment the tracer was released near the sediment water interface in this case the dynamics of vertical tracer spreading were opposite during the first few hours after tracer release diapycnal diffusivities were large subsequently decreasing as the tracer cloud drifted away from the lake boundary basin wide diapycnal diffusivities calculated from heat flux measurements based on temperature profiles obtained from thermistor chains or conductivity temperature depth casts agreed well with the values obtained from the vertical tracer diffusion after horizontal homogenization the results of the tracer experiments corroborate the hypothesis that diapycnal fluxes are determined predominantly by mixing in the bottom boundary region

turbulent mixing and exchange with interior waters on sloping boundaries abstractmicrostructure measurements along the axes of monterey and soquel submarine canyons reveal 200 300 m thick well stratified turbulent near bottom layers with average turbulent kinetic energy dissipation rates e 4 10 8 w kg 1 and eddy diffusivities k 16 10 4 m2 s 1 assuming mixing efficiency 0 2 to at least thalweg depths of 1200 m turbulent dissipation rates are an order of magnitude lower in overlying waters whereas buoyancy frequencies are only 25 higher well mixed bottom boundary layer thicknesses hn are an order of magnitude thinner than the stratified turbulent layer hn he because well stratified turbulent layers are commonly observed above slopes arguments that mixing efficiency should be reduced on sloping boundaries do not hold in cases of energetic internal wave generation or interaction with topography an advective diffusive balance is used to infer velocities and transports predicting horizontal upslope flows of 10 50 m day 1 extrapolating this estimate globa

a two dimensional model of boundary mixing the steady flow in and near a turbulent boundary layer on a sloping boundary is considered for a nonrotating stratified fluid it is shown that the effect of nonuniform stratification in the interior i e away from the turbulent layer is to induce a convergent divergent flow in the boundary layer which results in an inflow or outflow to the interior this inflow outflow acts in a divergent convergent manner on the interior isopycnals use of a filling box argument for the slow time variation of the interior then produces an approximate expression for an effective interior vertical diffusivity the parameter dependence of this diffusivity is very strong however with realistic geophysical values subject to the omission of rotation e g a mixed layer depth of 50 m munk s canonical value of 10 4 m2 s 1 can easily be achieved this work thus supports the view that boundary mixing is likely to be an important process in setting the vertical density profile in the ocean

internal waves and tides in the western weddell sea observations from ice station weddell the upper ocean current and temperature fields in the western weddell sea were measured from the drifting pack ice at ice station weddell 1 isw and nearby sites using a vertical profiler and an array of moored sensors in january june 1992 these data document the structure and variability of the internal gravity wave field and tidal currents in this remote region the variance of the internal wave continuum frequency n at isw was 0 2 0 6 of the garrett munk gm universal level for the first 60 days increasing to near gm levels during the final 10 days of the deployment in contrast the energy density at site c 50 km west of isw and farther up the continental slope was always near gm levels variations may be due to a combination of spatial and temporal gradients of the internal wave field at isw coherence between vertically separated sensors was used to estimate vertical wave number bandwidth energy and bandwidth estimates are compared with previous studies in both ice covered and temperate oceans using our measurements of the internal wave field and existing parameterizations of mixing we estimate the vertical heat flux from the warm deep water toward the surface at isw the upward heat flux due to mixing associated with the internal waves was about 1 w m 2 much less than the 20 w m 2 average flux required to balance the heat budget for the weddell gyre tidal currents contributed significantly to the total measured horizontal velocity variance the tides were primarily barotropic and increased toward the west in both the semidiurnal and diurnal frequency bands it is suggested that the stronger tidal currents to the west over the shallower water of the upper continental slope are indirectly responsible for the higher internal wave energy at site c relative to isw

an isopycnal view of near boundary mixing and associated flows abstract the effectiveness of mixing near a sloping boundary is reduced not just by the ratio of the stratification there to that in the interior but by the square of this ratio this result has previously been derived and interpreted by invoking the upgradient vertical buoyancy flux associated with secondary circulation as this opposes the downgradient vertical diffusive flux here it is shown that the result may be derived very simply by considering the diffusive flux across an isopycnal rather than a horizontal surface the reduction in the buoyancy flux comes from the increased isopycnal spacing and the reduced distance to the boundary derivation of the secondary circulation in the isopycnal diapycnal framework is more subtle however as it involves allowing for the curvilinear nature of the coordinates

mixing in the main thermocline abstract a series of profiles of velocity microstructure along 152 e in the western north pacific ocean were collected in may june 1982 large averaged turbulent dissipation rates found in the main thermocline 400 to 1000 m were determined by a combination of large independent estimates of and a greater rate of occurrence of turbulent events in the main thermocline than elsewhere concurrently we find that averaged values of exhibit a positive dependence on the buoyancy frequency n and that form an is best fit by 1 when only the data below 400 m are considered of the more than 5000 m of data collected below 1000 m depth 12 showed measurable turbulence and dominated the depth averages a deep ocean estimate of an upper bound to the eddy coefficient for vertical diffusion k is 10 4 m2 s 1 and not significantly different from the value estimated by munk the inferred dependence of the mass flux with depth indicates the relative significance of vertical mixing in the main thermocli

coastal boundary layer characteristics during summer stratification in lake ontario abstract simultaneous measurements of eulerian and lagrangian currents along the north shore of lake ontario are analyzed to provide the mean flow properties and horizontal turbulent exchange characteristics in the coastal boundary layer cbl the summer coastal boundary layer is characterized by a frictional boundary layer fbl of a width of 3 km in which shore and bottom friction affects the flow in this regime the currents are predominantly shore parallel and persistent the outer boundary layer also called an inertial boundary layer ibl typically of the order of 5 6 km wide is a consequence of the adjustment of inertial oscillations to the lateral boundary during the summer season within the cbl the current motions are associated with thermocline displacements the eastward westward wind stress causes thermocline elevation depression causing upwelling downwelling the mean subsurface westward currents associated with downwelling events are typically stronger in comparison to weak east