a study on wind driven circulation in the subarctic north pacific using topex poseidon altimeter data time dependent wind driven circulation in the subarctic region in the north pacific is investigated by using topex poseidon t p altimeter data and european centre for medium range weather forecasts ecmwf wind data for about 2 years the first empirical orthogonal function eof of the sea level anomaly sla without the variation related to the steric height change sla represents a basin sized oscillation which is associated with the spin up and spin down of the subarctic gyre moreover the time series of the first eof corresponds to the oyashio current variation measured by the moored current meter at about 1250 m depth the first and third eofs of the wind stress curl fields represent basin sized south north oscillations being associated with changes in intensity and the latitudinal position of the aleutian low time series of both the dominant eofs of the sla and the wind stress curl anomaly are correlated well which suggests that dominant variation of the sla is mainly controlled by the wind stress curl fields represented by the first and third eofs the time series of the first eof of the sla is in agreement with that of sverdrup transport estimated by the wind stress curl near 40 n with a correlation of 0 70 both standard deviations of the t p sla derived transports in the interior and the western boundary regions are consistent with that of the sverdrup transport in the same order of magnitude these results suggest that sea surface height variation in the subarctic north pacific is approximately explained by the time dependent wind driven circulation

comparison of topex sea surface heights and tide gauge sea levels topex sea surface height data from the first 300 days of the mission are compared to sea level data from 71 tide gauges the initial comparison uses sea surface height data processed according to standard procedures as defined in the users handbook it is found that the median correlations for island and for coastal tide gauges are 0 53 and 0 42 respectively the analogous rms differences between the two data sets are 7 9 and 10 4 cm the comparisons improve significantly when a 60 day harmonic is fit to the differences and removed this period captures aliased m2 and s2 tidal energy that is not removed by the tide model making this correction and smoothing the sea surface height data over 25 km along track segments results in median correlations of 0 58 and 0 46 for the islands and coastal stations and median rms differences of 5 8 and 7 7 cm respectively removing once per revolution signals from the sea surface heights results in degraded comparisons with the sea levels it is also found that a number of stations have poor comparisons due to propagating signals that introduce temporal lags between the altimeter and tide gauge time series a final comparison is made by eliminating stations where this propagation effect is large discarding two stations that are suspected to have problems with the sea level data smoothing over 10 day intervals and restricting attention to island gauges this results in a set of 552 data pairs that have a correlation of 0 66 and a rms difference of 4 3 cm the conclusion is that on timescales longer than about 10 days the rms sea surface height errors are less than or of the order of several centimeters

lithological anomalies in a relict coastal dune geophysical and paleoenvironmental markers 1 ground exposures of migration surfaces slipfaces of a relict holocene coastal dune along the southeastern baltic sea coast provide an ideal opportunity for establishing the causes of prominent reflections on geophysical profiles high amplitude reflections on high resolution ground penetrating radar gpr images correlate well with two major lithological anomalies 1 paleosols developed on dune slipfaces and 2 slipfaces consisting of heavy mineral concentrations hmcs paleosols serve as indicators of dune stability represent datable chronostratigraphic surfaces and help reconstruct dune paleo morphology hmcs have substantially higher magnetic susceptibility values than background quartz rich sands and where they are well developed can be also used for spatial correlation based on their occurrence at the study site these enriched horizons likely represent periods of increased wind activity storminess multiple hmcs upwind of paleosol p1 800 670 cal years bp likely reflect periods of intensified wind activity along the southeast baltic region during the medieval warm period

contributions of wind forcing waves and surface heating to sea surface height observations in the pacific ocean the dominant processes affecting sea surface height ssh variability observed by the topex poseidon altimeter vary regionally in the pacific baroclinic rossby waves equatorially trapped kelvin waves steric response to seasonal heating and the response to wind stress curl forcing are all important the steric response to surface heating dominates seasonal ssh variability in the subpolar gyre and the eastern subtropical gyre south of the kuroshio extension and south of 20 n in the eastern pacific the dominant contribution to ssh is from near annual period rossby waves to quantify the wave energy observed ssh was assimilated into a kinematic model of westward propagating waves these waves account for 70 of ssh variance between 10 s and 10 n but only 30 between 10 n and 30 n although wave energy in the eastern pacific is correlated with ssh anomalies at the equator the much larger wave energy in the western pacific is correlated with wind stress curl suggesting that the rossby waves there are locally forced in addition to these planetary waves the ocean response to wind forcing via ekman pumping is observed in several places specifically in the north equatorial current a quasi steady topographic sverdrup balance is detectable over most of the north pacific at latitudes as low as 10 15 n as well as in the south pacific where it is seen north of 50 s the decomposition of the ssh signal into propagating waves an ekman pumping response and sverdrup transport is consistent with the results from an isopycnal numerical model

multidecadal scale freshening at the salinity minimum in the western part of north pacific importance of wind driven cross gyre transport of subarctic water to the subtropical gyre abstractusing oceanographic observations and an eddy resolving ice ocean coupled model simulation from 1955 to 2004 the effects of the wind driven ocean circulation change that occurred in the late 1970s during multidecadal scale freshening of the north pacific intermediate water npiw at salinity minimum density 26 8 were investigated an analysis of the observations revealed that salinity decreased significantly at the density range of 26 6 26 8 in the western subtropical gyre including the mixed water region mwr the temporal variability of the salinity is dominated by the marked change in the late 1970s with results similar to the observations the model selectively forced by the interannual variability of the wind driven ocean circulation simulated significant freshening of the intermediate layer over the subtropical gyre the significant freshening is related to the increase in southward transport of the oyashio associated with the intensification of the aleutian low accompanying t

rheology of bubble bearing magmas the rheology of bubble bearing suspensions is investigated through a series of three dimensional boundary integral calculations in which the effects of bubble deformation volume fraction and shear rate are considered the behaviour of bubbles in viscous flows is characterized by the capillary number ca the ratio of viscous shear stresses that promote deformation to surface tension stresses that resist bubble deformation estimates of ca in natural lava flows are highly variable reflecting variations in shear rate and melt viscosity in the low capillary number limit e g in carbonatite flows bubbles remain spherical and may contribute greater shear stress to the suspension than in high capillary number flows in which bubble deformation is significant at higher ca deformed bubbles become aligned in the direction of flow and as a result contribute less shear stress to the suspension calculations indicate that the effective shear viscosity of bubbly suspensions at least for ca 0 5 is a weakly increasing function of volume fraction and that suspensions of bubbles are shear thinning field observations and qualitative arguments however suggest that for sufficiently large ca ca greater than about 1 the effective shear viscosity may be less than that of the suspending liquid bubbles reach their quasi steady deformed shapes after strains of order one for shorter times the continuous deformation of the bubbles results in continual changes of rheological properties in particular for small strains the effective shear viscosity of the suspension may be less than that of the liquid phase even for small ca results of this study may help explain previous experimental theoretical and field based observations regarding the effects of bubbles on flow rheology

the interaction of ash flows with ridges using both laboratory experiments and theoretical models we examine the different flow regimes that may develop when an ash flow encounters a ridge for very small ridges all the flow may pass over the ridge for intermediate size ridges the flow may be partially blocked with a fraction of the flow reflected upstream as a travelling bore in this case the remainder of the flow which does pass over the ridge is hydraulically controlled at the ridge crest finally if the ridge is sufficiently high then the flow will be totally blocked new laboratory experiments show that the sedimentation patterns associated with these flow regimes may be very different most importantly flows that involve partial blocking and the formation of upstream propagating bores display enhanced sedimentation upstream of the ridge analogous to valley ponded and caldera fill deposits in contrast under some circumstances if the flow is able to scale a ridge the deposit may be relatively unaffected by the presence of the ridge the minimum ridge height that leads to total blocking of the flow increases with mass eruption rate and has a complex variation with distance from the source in a one dimensional channel the minimum ridge height that causes blocking increases with distance downstream this is because the flow becomes less dense through sedimentation of particles and entrainment of air and so requires less energy to scale a ridge of a particular height in axisymmetric flow the minimum ridge height initially decreases with distance downstream as the flow spreads radially but subsequently increases as the flow becomes less dense through sedimentation and entrainment a new quantitative model of dilute ash flows propagating over ridges indicates that flows with mass fluxes in excess of 108 109 kg s can partially scale barriers as high as 1000 m at distances of tens of kilometres from the source whereas smaller flows are likely to be totally blocked by such an obstacle our results shed new insight on the possible long range transport mechanism of several large flows including the ata fisher and aniakchak pyroclastic flows

flow fields around the emperor seamounts detected from current data 1 bathymetric influences of the emperor seamounts ess on the local and large scale flow fields in the subarctic north pacific were investigated by analyzing data of directly measured velocity obtained using argo floats near surface buoys and moored current meters the local influences were evident in notable deflections of two relatively strong 0 05 m s 1 eastward flows over ess a taylor cap induced by the eastward flow impinging against the nintoku seamount around 42 0 n 170 5 e was clearly identified in the climatological flow field at 1000 m depth this flow pattern was also identified in the near surface flow field 15 m depth and dynamic height field at 200 dbar relative to 2000 dbar indicating the taylor cap is stable or frequently generated and extends to the surface an anticyclonic flow was found over the suiko seamount around 45 0 n 170 5 e the influences on the large scale flow field were found in data obtained from current meters moored over the southeastern flank of the suiko seamount and argo float trajectories these data indicate for the first time from velocity observations that there is a seasonally varying boundary current along the eastern side of ess partially compensating for the sverdrup transport to the east of ess and hence the seasonally varying component of the subarctic gyre in the north pacific is divided into two subgyres by ess

quasi stationary jets transporting surface warm waters across the transition zone between the subtropical and the subarctic gyres in the north pacific 1 surface flow jets and associated sea surface temperature sst distribution are investigated in the northwestern north pacific using satellite derived surface currents and sst data that can resolve fine spatial scale structure the combined use of these data reveals warm tongue phenomena driven by surface geostrophic jets which extend northeastward in the kuroshio oyashio transition area they roughly coincide with the subarctic front saf defined as the 4 c isotherm at 100 m depth the phenomena appear throughout the year with seasonal cycles which do not correspond with that of the subarctic north pacific their positions are affected by bottom topography so that their quasi stationary and consistent features are suggested thus it is implied that these jets play an important role in transporting warm waters toward the subarctic region the time series of sst and current fields describe the jets year to year variability involving some changes in strength and connections with the kuroshio extension ke and demonstrate the effects of advection by the jets on sst fields when ke extends northward at its crests for 1999 2002 one of the jets along saf simultaneously strengthens resulting in high sst region directly over and along the south side of the jet hydrographic data show warm saline water intrusions along the jets their mean fields also reveal that these jets are vertically well developed forming a boundary between the subtropical and subarctic gyres in the north pacific

crystal settling in a vigorously converting magma chamber there has been much debate concerning the mechanism of fractional crystallization in magma chambers the traditional hypothesis of crystal settling has been widely replaced by the concept of in situ crystallization coupled with compositional convection observations from layered intrusions however are equivocal1 4 doubts have been raised about crystal settling on theoretical grounds because convective velocities in magma chambers are often much greater than the crystal settling velocities predicted by stokes law5 but there has been no experimental study of crystal settling in such vigorous convection here we present physical considerations and laboratory experiments which show that the phenomenon of particle settling in these conditions can be accounted for by a simple theory application of this theory to crystal settling in magma chambers suggests that crystal settling may be an efficient differentiation mechanism at least in basaltic magma chambers despite large convective velocities

on the interaction between convection and crystallization in cooling magma chambers abstract we investigate the interaction of thermal convection and crystallization in large aspect ratio magma chambers because nucleation requires a finite amount of undercooling crystallization is not instantaneous for typical values of the rates of nucleation and crystal growth the characteristic time scale of crystallization is about 10 3 10 4 s roof convection is characterized by the quasi periodic formation and instability of a cold boundary layer its characteristic time scale depends on viscosity and ranges from about 10 2 s for basaltic magmas to about 10 7 s for granitic magmas hence depending on magma viscosity convective instability occurs at different stages of crystallization a single non dimensional number is defined to characterize the different modes of interaction between convection and crystallization using realistic functions for the rates of nucleation and crystal growth we integrate numerically the heat equation until the onset of convective instability we determine both temperature and crystal content in the thermal boundary layer crystallization leads to a dramatic increase of viscosity which acts to stabilize part of the boundary layer against instability we compute the effective temperature contrast driving thermal convection and show that it varies as a function of magma viscosity and hence composition in magmas with viscosities higher than 10 5 poise the temperature contrast driving convection is very small hence thermal convection is weak in low viscosity magmas convective breakdown occurs before the completion of crystallization and involves partially crystallized magma the convective regime is thus characterized by descending crystal bearing plumes and bottom crystallization proceeds both by in situ nucleation and deposition from the plumes we suggest that this is the origin of intermittent layering a form of rhythmic layering described in the skaergaard and other complexes we show that this regime occurs in basic magmas only at temperatures close to the liquidus and never occurs in viscous magmas this may explain why intermittent layering is observed only in a few specific cases

settling driven convection a mechanism of sedimentation from stratified fluids convection driven by sediment particles may play an important role in sedimentation from the base of buoyant hypopycnal plumes for example fluvial plumes in stratified estuaries and lakes black smokers on the ocean floor volcanic clouds and coastal currents in addition to the well known double diffusive convection mechanism another mode of convective instability development is by settling across the density interface we performed laboratory experiments to investigate this fingering convective instability mechanism and its effect on particle distribution in the water column and deposition at the bed a simple theoretical model of finger formation at a fluid density interface is developed based on an analogy with thermal plume formation at a flat heated plate this model which involves a thickening interface layer that becomes gravitationally unstable relative to the ambient fluid is in good agreement with measurements of finger size and instability wavelength from visualization experiments since fingering at the density interface drives larger scale convection in the fluid below a mass balance model of the lower layer assuming strong mixing i e uniform sediment concentration is successfully applied to predict sediment concentration in the water column and deposition at the bed strong mixing can be assumed since convective velocities are usually much greater than the particle fall velocities as convection proceeds the sediment concentrations in the two layers approach each other and convection will die out using the model equations we develop analytical expressions for the time when convection ceases and the portion of sediment remaining in the water column

coupled wind forced controls of the bering chukchi shelf circulation and the bering strait throughflow ekman transport continental shelf waves and variations of the pacific arctic sea surface height gradient abstract we develop a conceptual model of the closely co dependent bering shelf bering strait and chukchi shelf circulation fields by evaluating the effects of wind stress over the north pacific and western arctic using atmospheric reanalyses current meter observations satellite based sea surface height ssh measurements hydrographic profiles and numerical model integrations this conceptual model suggests bering strait transport anomalies are primarily set by the longitudinal location of the aleutian low which drives oppositely signed anomalies at synoptic and annual time scales synoptic time scale variations in shelf currents result from local wind forcing and remotely generated continental shelf waves whereas annual variations are driven by basin scale adjustments to wind stress that alter the magnitude of the along strait meridional pressure gradient in particular we show that storms centered over the bering sea excite continental shelf waves on the eastern bering shelf that carry northward velocity anomalies northward through bering strait and along the chukchi coast the integrated effect of these storms tends to decrease the northward bering strait transport at annual to decadal time scales by imposing cyclonic wind stress curl over the aleutian basin and the western subarctic gyre ekman suction then increases the water column density through isopycnal uplift thereby decreasing the dynamic height sea surface height and along strait pressure gradient storms displaced eastward over the gulf of alaska generate an opposite set of bering shelf and aleutian basin responses while ekman pumping controls canada basin dynamic heights proshutinsky et al 2002 we do not find evidence for a strong relation between beaufort gyre sea surface height variations and the annually averaged bering strait throughflow over the western chukchi and east siberian seas easterly winds promote coastal divergence which also increases the along strait pressure head as well as generates shelf waves that impinge upon bering strait from the northwest

characteristics of sediments and their dispersal systems along the shelf and slope of an active forearc margin eastern hokkaido northern japan abstract this study revealed sediment distributions and their dispersal systems in a shelf slope setting along an active forearc margin off eastern hokkaido northern japan where the pacific plate is being subducted beneath the okhotsk north american plate at the 7 km deep kuril trench the findings were based on analyses of the textures and structures of surface sediments components of the sampled sand fractions high resolution acoustic reflection records and sediment budgets the studied margin has a 20 30 km wide shelf and steep 5 10 slope marked by faults and folds associated with transpressional tectonics the shelf sediments are classified into gravelly coarse to fine sand from the shelf edge to the uppermost slope 110 1000 m water depth gravel and coarse sand on the shelf off hanasaki fine sand on the middle outer shelf off kiritappu and very fine sand on the shelf off akkeshi the coarse sediments on the eastern shelf off hanasaki and the shelf margin are interpreted to represent lag deposits from coastal erosion associated with a post glacial transgression across topographic highs the two depocenters of shelf sediments subsequent to the last glacial maximum are situated in the middle outer shelf off kiritappu and in the inner middle shelf off akkeshi these are interpreted as transgressive highstand sequences whose locations were controlled by ridges on the shelf margin and topographic highs on the shelf the shelf sediment thickness reaches 20 m and the total volume is estimated at ca 6 km3 the slope sediments are grouped into medium fine sand on the uppermost and upper slopes 150 2000 m water depth and mud dominated sediments on the upper to middle slope 1000 3000 m water depth the sandy sediments on the slope at water depths greater than 1000 m are regarded as being derived from the shelf break by gravitational redistribution the occurrence of diamictite like sediments around gullies that incise into the slope indicates that mass movement and sediment gravity flows play an important role in the redistribution of sediments upon the slope on the upper middle slope hemipelagic fallout and advection of turbid water from the shelf edge provide a supply of suspended material the main contributor of sediment supply to the area is coastal erosion 1 81 mt y 1 along with a lesser contribution from fluvial input 0 10 mt y 1 during the latest quaternary the rates of sediment accumulation upon the shelf are estimated to have been 0 47 mt y 1 the remainder of the material transported into the sea is probably redistributed to deeper parts of the slope via gravitational sediment flows or transported outside of the study area by alongshore and tidal currents the studied shelf that kept less than a quarter of the mass from land is comparable with other active margin shelves of new zealand and california although they are fed by high sediment laden rivers

influence of okhotsk sea intermediate water on the oyashio and north pacific intermediate water 1 the volume transport between the okhotsk sea and western subarctic north pacific is estimated on the basis of direct current measurements made by a lowered acoustic doppler current profiler ladcp and hydrographic data taken in august and september 1999 near the kuril islands the estimated southwestward oyashio transport was 11 12 sv 106 m3 s in the density range of 26 7 27 4 the net transport of the okhotsk sea water osw was 3 4 sv of which 1 3 sv was coming out through the kruzenshterna strait and 2 1 sv was coming out through the bussol strait a bidirectional flow was observed in the bussol strait inflow in the northern part of the strait and outflow in the southern part 0 6 sv of osw recirculated along the western subarctic gyre the remaining 2 8 sv of osw could contribute to the formation of north pacific intermediate water as a cross subarctic front transport along the coast 1 4 sv and across the offshore saf 1 4 sv the production rate of the dense shelf water dsw through sea ice formation was estimated to be at least 1 1 sv when the intermediate osw is formed through the mixing between cold and fresh dsw and warm and salty waters from the pacific and japan sea 16 8 tw 1012 w of heat 0 007 sv of freshwater and 2 3 105 kg s of salt are exchanged the net flux of oxygen and anthropogenic co2 ex co2 from the okhotsk sea into the pacific in 26 7 27 4 is estimated to be 10 5 and 2 1 tmol yr 0 025 gtc yr respectively the ex co2 transported by osw accounts for about 10 of the accumulation of ex co2 in the subarctic and subtropical pacific

numerical experiments on the seasonal variations of the oyashio near the east coast of japan abstract seasonal variations of the oyashio near the east coast of japan are examined using a simple layered model with a localized diapycnal transport due to the strong tidal mixing around the kuril islands the modeled southernmost latitude is located at around 40 n in spring and 42 n in autumn the southwestward oyashio transport in the upper layers and depth integrated transport become large small during winter spring summer autumn these results are in agreement with observations the seasonal variation of the southernmost latitude is mainly caused by the baroclinic velocity anomalies off tohoku and hokkaido japan which have been excited by the wind stress changes along the west coast of north america the kamchatka peninsula and the model northern boundary this is different from the previous studies that emphasized the importance of direct barotropic response of the ocean to the basin scale wind stress changes for comparison an additional experiment in which the diapycnal transport around

tracing sediment movement in interrill overland flow on a semi arid grassland hillslope using magnetic susceptibility experiments were undertaken to determine the feasibility of tracing sediment movement in interrill overland flow crushed magnetite was introduced as a source line 10 cm wide by 8 m long on a runoff plot 18 m wide by 29 m long located in southern arizona initial magnetic susceptibilities along this source line and along three transects located 0 25 2 95 and 5 m downslope of the source line were measured movement of the magnetite in response to three rainfall simulation experiments was monitored during the first two experiments overland flow discharge was sampled at miniature flumes located along two cross sections on the plot downslope of the source line and at a supercritical flume at the plot outlet magnetic susceptibilities along the source line and transects were measured after all three experiments results show that the magnetite moves very early in the experiments and that it reaches one of the flumes 2 m downslope of the source line in 3 min most of the tracer moves a very short distance 29 7 per cent is deposited within 25 cm of the source line and only 2 2 per cent is deposited 2 95 m away the deposition rate appears to decrease exponentially away from the source line very little magnetite is recorded in the flow through the miniature flumes in general it makes up less than 1 per cent of the total sediment load no temporal pattern in these percentages is observed magnetite appears to be an effective tracer of sediment movement in interrill overland flow though its higher density than natural soil may affect its detachment and transport

aeolian processes and the biosphere ravi s d odorico p breshears d d field j p goudie a s huxman t e li j okin g s swap r j thomas a d pelt s v whicker j j zobeck t m 2011 aeolian processes and the biosphere reviews of geophysics 49 3

shelf slope sedimentation during the late quaternary on the southwestern kuril forearc margin northern japan abstract we studied an active forearc margin off eastern hokkaido northern japan to identify the main influences on stratigraphic development from the last glacial to the present highstand this paper presents new data on the environment texture and sedimentation rates of forearc shelf slope sediments based on more than 300 samples of seafloor sediments and densely gridded sub bottom profiling records lowstand sedimentary wedges developed upon the shelf margins in areas with a large sediment supply and without incising canyons the transgressive and highstand deposits formed on the shelf in extensive low gradient and topographically low areas the narrow shelf is covered by sandy sediments where winnowed fines are likely to have escaped to the slope via gravity driven across shelf transport or ocean current induced along shelf transport the slope has a mid slope mud belt at water depths of 700 1600 m the sedimentation rates on the slope subsequent to 15 ka the late transgressive to highstand stage were just 10 70 of the rates prior to this period these changes in sedimentation rates are ascribed to spatially variable topography high sedimentation rates were maintained at topographically low and gently sloping areas even during highstand periods due to concentrations of nepheloid layers or deposition via sediment gravity flows on the other hand low sedimentation rates were recognized on topographic highs of interfluves on the upper slope or on axes of anticlines where main flows or overspills of turbidity currents decreased as sealevel rose these results suggest that sedimentologic and stratigraphic variations are tied to variations in the physical configuration of the shelf slope system being influenced by the local topography in addition to the climatic and oceanographic processes

evidence of time dependent sverdrup circulation in the south pacific from the seasat scatterometer and altimeter abstract seasat scatterometer and altimeter data are analyzed to investigate time dependent sverdrup dynamics in the southern ocean 40 s to 60 s over seasonal time scales sverdrup dynamics are shown to be inadequate to describe the circulation in the south atlantic and indian oceans the sverdrup circulation in the south pacific is reasonable north of 55 s the changes in sverdrup circulation from july to september 1978 indicate an eastward acceleration along 55 s and westward acceleration along 40 s suggesting a southward shift in the subpolar eastward flow sea level in the south pacific is estimated for july and september 1978 from scatterometer vector wind data based on sverdrup dynamics assuming a flat bottom ocean with barotropic flow the changes in sverdrup sea level are compared with the changes in sea level observed by the altimeter for the same time period both estimates indicate a rise in sea level along a zonal band centered at about 50 s this sea level rise inferred from both the scatt

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

fluid motions and compositional gradients produced by crystallization or melting at vertical boundaries the results of a continuing series of laboratory experiments designed to model the fluid motions which accompany crystallization are both described and related in a preliminary way to prototype flows in magma chambers previous experiments have demonstrated the importance of compositional inhomogeneity produced by crystallization and melting in a thermal gradient and coupled with double diffusive effects in driving convective flows which result in thermal and compositional stratification in an originally homogeneous fluid the present experiments examine effects produced in tanks cooled at the side by the upward flow of a less dense boundary layer depleted in the crystallizing component as crystals grow on the side wall these processes are examined in simple two and three component aqueous systems h2o na2co3 h2o na2co3 k2co3 h2o cuso4 na2so4 with one and two crystallizing phases in each of these systems an initially downward flow of a cooled boundary layer against the side wall is reversed as crystallization commences and depletes the boundary layer in the crystallizing component accumulation of this cooler but lighter depleted fluid at the top of the chamber produces thermal and compositional layering by a filling box mechanism partly modified by interchange between the boundary layer and the convecting layers outside when more than one component is present in the solution the crystallization process produces a differentiated fluid column i e one with compositional gradients which are different for each of the components the compositional and thermal distributions within the fluid change with time but finally appear to reach a steady state these distributions are the integrated result of compositional changes produced by crystallization from a thin boundary layer a small proportion of the bulk fluid which evolves in composition and temperature independently of the bulk fluid in a manner controlled by the dynamics of the system the paths of fluid evolution and the resulting sequence and abundance of crystalline products are very different from those predicted on the basis of simple thermally driven crystallization in the static system disequilibrium effects probably involving different kinetics of crystallization of different crystals in part determine crystallization in the experimental system these may or may not be important in real magmatic systems there is still much to learn before even the behaviour in these simple experimental systems is understood fully and the application of the results to the interpretation of the behaviour in real magma chambers in even further away however it is apparent that dynamic effects provide an additional degree of freedom in crystallization processes and allow evolution of small increments of solution to compositions much further along crystallization paths than that allowed in static equilibrium systems petrologists will have to free their thinking from classical constraints of static systems in order to interpret many magmatic phenomena

a note on the barotropic response of sea level to time dependent wind forcing this study examines the extent to which sea level variations at periods between 30 days and 1 year and spatial scales greater than 1000 km can be described by the wind driven linear barotropic vorticity dynamics the topex poseidon altimetric observations of sea level and the wind products of the national meteorological center are used as the database for the study each term of the linear barotropic vorticity equation was evaluated by averaging over regions of 10 10 in most of the open ocean the result of the analysis suggests that the sea level variabilities at the scales considered cannot be fully described by the equation the apparent net vorticity change is more than what can be explained by the local wind stress curl in the few regions where the wind stress curl is strong enough to balance the vorticity budget predominantly in the northeast pacific and the southeast pacific the balance is basically achieved in terms of the time dependent topographic sverdrup relation namely the balance between the advection of the planetary vorticity plus the topography induced vorticity and the forcing by the wind stress curl

mixing of stratified liquids by the motion of gas bubbles application to magma mixing mafic magma underlying more silicic magma in a reservoir can exsolve volatiles as it crystallizes forming bubbles that segregate upwards to the interface with the overlying silicic magma we describe laboratory experiments designed to investigate how gas bubbles migrate into the more viscous upper layer in one regime bubbles move individually across the interface entraining a small quantity of lower layer fluid and the two layers become progressively stirred into a homogeneous mixture in a second regime bubbles form a thin foam layer at the interface which becomes gravitationally unstable giving rise to two phase plumes which rise and produce a coarse mixture of the liquids for a given viscosity ratio the transition between these regimes occurs when the gas flux is greater than a critical value which we found to decrease with increasing viscosity ratio we estimate the critical gas flux for magmatic conditions and how vesiculation may vary with pressure degree of crystallization and the composition of volatile components mafic inclusions which are often found in silicic to intermediate lavas can form in the plume regime analysis of the instability of the foam predicts wavelengths of between 1 cm and 1 m which is consistent with the observed sizes of inclusions volatiles from the mafic magma may be efficiently transported by this mechanism into the viscous silicic magma as bubble plumes despite low stokes velocities for individual vesicles at small viscosity ratios or low gas fluxes the bubbling regime can produce hybrid magmas

seasonal variation in the in and outflow of the okhotsk sea with the north pacific abstract this paper examines the seasonal variation in the in and outflow of the okhotsk sea with the pacific mainly based on profiling float and satellite altimeter data the motions of the floats at depths of 500 750 m show that the waters of the okhotsk tend to flow out to the pacific through the southern kuril straits mostly bussol strait in winter seasons november march based on data from the floats exiting the sea the mean residence time of the intermediate water in the kuril basin is estimated as about one year isopycnal analysis from the profiling data shows that in the mid eastern area of the okhotsk sea potential temperature of the intermediate water with 26 6 27 2 increases by 0 2 0 5 c in every spring suggesting the inflow from the pacific in the preceding season these suggest that the in and outflow predominantly occurs during winter with the inflow at the northern straits and outflow at the southern straits the surface current field inferred from satellite altimeter data also shows that the inflow to the sea of okhotsk through the northern straits is strengthened in winter linked with strengthening of the east kamchatka current ekc from yearly anomalies of the altimeter data the winter inflow to the okhotsk through the northern straits is significantly correlated with the ekc and sverdrup transport over the north pacific further interannual variations in property of okhotsk sea intermediate water appear to be related with the ekc and wind stress over the north pacific in winter possibly through the change in inflowing pacific water transport these suggest that the seasonal and interannual variations of the in and outflow are to some extent controlled by the large scale wind stress over the north pacific being consistent with island rule qualitatively

evolution of crystal settling in magma chamber convection abstract the motion of negatively buoyant particles embedded within kinematically prescribed convective velocity fields is used to study the evolution of crystal settling in magma chambers we consider the effects of stokesian settling velocity crystal growth aspect ratio of the convective domain and the site of crystal nucleation on mixing and transport of heavy crystals in this system the percentage of particles retained in a convecting fluid is very sensitive to the site of nucleation particles nucleating along the cold roof or within the wall boundary layers are generally not retained as a consequence crystal settling can occur even in rapidly convecting magma chambers equilibrium crystal densities are reached relatively quickly within one overturn and the distribution of particles deposited on the bottom of the chamber is always asymmetric this feature may facilitate the formation of primary sedimentary structures in plutons laboratory experiments using small negatively buoyant spheres in a highly viscous fluid with axisymmetric thermal convection confirm the basic predictions of this model

global statistical analysis of topex and poseidon data a global statistical analysis of the first 10 months of topex poseidon merged geophysical data records is presented the global crossover analysis using the cartwright and ray 1990 cr tide model and gaspar et al this issue electromagnetic bias parameterization yields a sea level rms crossover difference of 10 05 cm 10 15 cm and 10 15 cm for topex topex poseidon poseidon and topex poseidon crossovers respectively all geophysical corrections give reductions in the crossover differences the most significant being with respect to ocean tides solid earth tide and inverse barometer effect based on topex poseidon crossovers and repeat track differences we estimate the relative bias between topex and poseidon at about 15 5 1 cm this value is dependent however to the electromagnetic bias corrections used an orbit error reduction method based on global minimization of crossover differences over one cycle yields an orbit error of about 3 cm rms this is probably an upper estimate of the orbit error since the estimation absorbs other altimetric signals the rms crossover difference is reduced to 8 8 cm after adjustment a repeat track analysis is then performed using the cr tide model in regions of high mesoscale variability the rms sea level variability agrees well with the geosat results tidal errors are also clearly evidenced a recent tide model ma et al this issue determined from topex poseidon data considerably improves the rms sea level variability the reduction of sea level variance is 4 cm 2 on average but can reach 8 cm 2 in the southeast pacific southeast atlantic and indian oceans the rms sea level variability thus decreases from 6 cm to only 4 cm in quiet ocean regions the large scale sea level variations over these first 10 months most likely show for the first time the global annual cycle of sea level finally we analyze the topex and poseidon sea level anomaly wavenumber spectral characteristics topex and poseidon have identical spectral characteristics at low wavenumbers for wavelengths shorter than 100 km however poseidon spectra are more energetic this is probably related to the topex tracker characteristics and to the way the acceleration correction is made in the geophysical data records poseidon repeat track noise level is estimated at about 3 cm for a 1 s average the topex repeat track noise level is about 1 8 cm rms but this probably corresponds to averages over several seconds

sedimentation from turbulent jets and plumes theoretical models are developed for the sedimentation from the margins of a particle laden axisymmetric turbulent buoyant plume in a still environment and for an axisymmetric turbulent momentum jet the models assume that the mass of each individual size fraction of sediment carried in a parcel of fluid decreases exponentially with time for relatively coarse particles the fallout models predict that the sediment deposition beyond a distance r on the ground expressed in log units should decay linearly with distance away from the vent for the momentum jet and should decrease with r1 3 for the buoyant plume the exponential decay constant j is proportional to the terminal fall velocity vt of the particles in both cases and inversely proportional to the square root of the initial momentum flux m0 for the jet fallout jj vtmo 1 2 and to the third power of the initial buoyancy flux fo for the plume fallout jp vtfo 1 3 smaller particles are affected by reentrainment caused by the turbulent eddies sweeping ambient fluid back into the plume or jet and thus reincorporating some particles that were released from the flow at greater heights this is taken into account by introducing a reentrainment coefficient into the theoretical models with the assumption that the coefficient has a constant value for a plume of given strength in new experiments fallout occurs from the margins of particle laden fresh water buoyant jets and plumes in a tank of salty water and sedimentation is measured on the tank floor two experiments were weakly affected by reentrainment and show excellent agreement with the simple theory for smaller particles and increasingly buoyant plumes and strong jets particle reentrainment is important the experimental data are fitted by the new reentrainment theory confirming that values of the reentrainment coefficient are approximately constant for a given flow a settling number is defined as the ratio of the characteristic velocity of the jet or plume to the particle settling velocity for 1 reentrainment seems to reach an equilibrium state for which the reentrainment coefficient is a constant of value 0 1 for jets and 0 4 for plumes irrespective of flow strength or particle size the plume experiments indicate that the value of the reentrainment coefficient is strongly dependent on plume strength and particle size for slightly less than 1 the general principles of sedimentation from turbulent plumes and jets are applied to the fallout of pumice from volcanic eruption columns and of metalliferous particles from black smokers on the ocean floor for volcanic eruptions the results provide an explanation for the near vent overthickening of tephra fall deposits and imply that lithic and pumice fragments from small lapilli up to at least 1 m diameter blocks are efficiently reentrained into eruption columns the size of particles reentrained in hydrothermal plumes is predicted to vary from less than 100 m in weakly buoyant plumes up to over 1000 m in megaplumes

addressing complexity in laboratory experiments the scaling of dilute multiphase flows in magmatic systems the kinematic and dynamic scaling of dilute multiphase mixtures in magmatic systems is the only guarantee for the geological verisimilitude of laboratory experiments we present scaling relations that can provide a more complete framework to scale dilute magmatic systems because they explicitly take into account the complexity caused by the feedback between particles crystal bubble or pyroclast and the continuous phase liquid or gas we consider three canonical igneous systems magma chambers volcanic plumes and pyroclastic surges and we provide estimates of the proposed scaling relations for published experiments on those systems dilute magmatic mixtures can display a range of distinct dynamical regimes that we characterize with a combination of average eulerian properties and instantaneous lagrangian variables the eulerian properties of the mixtures yield the reynolds number re which indicates the level of unsteadiness in the continuous phase the lagrangian acceleration of particles is a function of the viscous drag and gravity forces and from these two forces are derived the stokes number st and the stability number rt two dimensionless numbers that describe the dynamic behavior of the particles within the mixture the compilation of 17 experimental studies relevant for pyroclastic surges and volcanic plumes indicates that there is a need for experiments above the mixing transition ren10 4 and for scaling st and rt among the particle dynamic regimes present in surges and plumes some deserve special attention such as the role of mesoscale structures on transport and sedimentary processes or the consequences of the transition to turbulence on particle gathering and dispersal the compilation of seven experimental studies relevant to magma bodies indicates that in the laminar regime crystals mostly follow the motion of the melt and thus the physical state of the system can be approximated as single phase in the transition to turbulence magmas can feature spatially heterogeneous distributions of laminar regions and important velocity gradients this heterogeneity has a strong potential for crystals sorting in conclusion the re st rt framework demonstrates

determination of ocean tides from the first year of topex poseidon altimeter measurements an improved geocentric global ocean tide model has been determined using 1 year of topex poseidon altimeter measurements to provide corrections to the cartwright and ray 1991 model cr91 the corrections were determined on a 3 3 grid using both the harmonic analysis method and the response method the two approaches produce similar solutions the effect on the tide solution of simultaneously adjusting radial orbit correction parameters using altimeter measurements was examined four semidiurnal n2 m2 s2 and k2 four diurnal q1 o1 p1 and k1 and three long period ssa mm and m constituents along with the variation at the annual frequency were included in the harmonic analysis solution the observed annual variation represents the first global measurement describing accurate seasonal changes of the ocean during an el nino year the corrections to the m2 constituent have an rms of 3 6 cm and display a clear banding pattern with regional highs and lows reaching 8 cm the improved tide model reduces the weighted altimeter crossover residual from 9 8 cm rms when the cr91 tide model is used to 8 2 cm rms comparison of the improved model to pelagic tidal constants determined from 80 tide gauges gives rms differences of 2 7 cm for m2 and 1 7 cm for k1 comparable values when the cr91 model is used are 3 9 cm and 2 0 cm respectively examination of topex poseidon sea level anomaly variations using the new tide model further confirms that the tide model has been improved

influence of the meridional shifts of the kuroshio and the oyashio extensions on the atmospheric circulation abstract the meridional shifts of the oyashio extension oe and of the kuroshio extension ke as derived from high resolution monthly sea surface temperature sst anomalies in 1982 2008 and historical temperature profiles in 1979 2007 respectively are shown based on lagged regression analysis to significantly influence the large scale atmospheric circulation the signals are independent from the enso teleconnections which were removed by seasonally varying asymmetric regression onto the first three principal components of the tropical pacific sst anomalies the response to the meridional shifts of the oe front is equivalent barotropic and broadly resembles the north pacific oscillation western pacific pattern in a positive phase for a northward frontal displacement the response may reach 35 m at 250 hpa for a typical oe shift a strong sensitivity since the associated sst anomaly is 0 5 k however the amplitude but not the pattern or statistical significance strongly depends on the lag and an

large scale sea level variations and associated atmospheric forcing in the subtropical north east atlantic ocean abstract the large scale sea level variations in the subtropical north eastern atlantic ocean are characterised by a predominant seasonal fluctuation analysis of 6 years 1993 98 of combined topex poseidon and ers 1 2 altimetric data together with data of concurrent oceanic surface geophysical fields ecmwf net heat fluxes ecmwf winds and reynolds sea surface temperature reveals that the dominant physical forcing of sea level variations on an annual timescale is the air sea net heat fluxes this local forcing generates a seasonal ocean steric response whose amplitude of the order of 4 5 cm varies spatially within the studied area and temporally over the 6 year period the residual variability is mainly characterised by a non seasonal signal which is observed northwards of the azores current 34 n and its time variation resembles that of the north atlantic oscillation nao a combination of steric effects wind induced heat fluxes and wind effects barotropic sverdrup response appear to explain this signal some evidence of a local ekman pumping response is also found regionally both in the seasonal and non seasonal variations of the observed sea level at the interannual timescale an overall sea level trend with a mean rate of 0 5 cm year is detected however the magnitude of the trend varies locally so that the entire sea surface appears to undergo a general tilt which extends beyond the studied area superimposed on this long term trend a sharp temporal sea level rise occurs in 1995 mainly between the azores and madeira islands all together these low frequency sea level variations seem to co vary with the large scale sea surface temperature sst variations this implies a comparable evolution of the sea level with the upper ocean thermal content which suggests a contribution from steric effects a weaker situation is observed in the northern area indicating a possible low frequency wind forcing enhanced contribution

a dynamically consistent analysis of the mesoscale eddy field at the western north pacific subarctic front 1 in this study we analyze the energetics of the quasigeostrophic qg currents observed in the course of an extensive soviet field experiment in 1987 the analyzed data span over the period of 1 month and cover the region 37 5 42 5 n 151 5 158 e at an average horizontal resolution of 35 km the processed data set includes the results of measurements at 668 hydrographic stations 118 moorings geosat sea surface height anomalies ecmwf winds and etop05 bottom topography a variational data assimilation method is employed to interpolate observations onto a regular space time grid an ensemble average over optimized ocean states is utilized to estimate posterior error bars assimilation has shown that the observed mesoscale structures are well described by qg dynamics which can explain 80 85 of the variability in the velocity and density fields the model data misfits lie within the observational error bars for all the data types used in assimilation the standard laplacian type parameterization of the small scale processes was found to be inconsistent with observations as the least model data misfits were obtained with zero diffusivity coefficients analysis of the interpolated patterns revealed a pronounced mesoscale mixing event characterized by the development of a warm streamer swirling around the upper cold core of an old anticyclonic kuroshio extension eddy the process was accompanied by a fast northwestward displacement of the eddy and induced detachment of a warm elongated vortex from its eastern rim within a week the vortex penetrated northward into the subarctic zone and eventually split into several smaller scale eddies energy analysis of the optimal solution indicates that baroclinic instability is the likely source of their energy computation of energy exchanges between depth averaged and shear components of the observed currents reveals the vertical energy cascade barotropization of the shear flow at a rate of 29 4 10 7 cm2 s 3 and the weaker kinetic energy transfer of opposite sign due to topographic interaction mean currents in the region are baroclinically unstable with an estimate of the available potential energy flux from the mean current to the eddies 53 8 10 7 cm2 s 3 potential enstrophy is transferred to mesoscale at a rate of 33 7 10 19 s 3 these figures can be considered as experimental evidence of the properties of free geostrophic turbulence which were predicted by theory and observed in numerical experiments

coherent sea level variation in and around the sea of okhotsk abstract we investigated the seasonal and interannual variations of the sea level in and around the sea of okhotsk and their causes based on tide gauge and satellite altimeter data the sea level all along the coastal region of the sea of okhotsk is found to be dominated by the seasonal variation with a maximum in winter and a minimum in summer which cannot be explained by the annual cycle of atmospheric heat flux and pressure this sea level variation appears to reflect ocean current variations both the arrested topographic waves atws caused by alongshore wind stress and the sverdrup transport by wind stress curl show corresponding seasonal variations seasonal amplitude of the sea level is relatively large along sakhalin island with a tendency of a larger amplitude toward the south this meridional dependence is consistent with the atws but not with the sverdrup transport in the sea of okhotsk seasonal variation of the geostrophic current velocity expected from the sea level variation is comparable to that of the observed nearshore current and is consistent with the theoretical atw transport it is also revealed that on an interannual timescale the wintertime sea level fluctuates quite coherently all around the sea of okhotsk and further along the east kamchatka and oyashio coasts in the north pacific the altimeter data clearly show that this coherent sea level variation is trapped over the coastal and continental shelf regions with depths shallower than 1000 m the wintertime sea levels have a higher correlation with the atw transport than with the sverdrup transport in the sea of okhotsk and the upstream east kamchatka coast all these suggest that the interannual sea level variation along the coastal and shelf regions in winter as well as the seasonal variation is mainly caused by the atws coastal trapped current forced by the alongshore wind stress the wintertime sverdrup transport raised by the previous studies is the secondary contributor to these variations

deposition pattern and sources of palynomorphs on the continental margin off hokkaido island northwest pacific abstract hokkaido island in northern japan is located in a cool temperate to boreal climate zone influenced by summer monsoons and typhoons during summer autumn while its eastern area is influenced by the subarctic oyashio current palynomorph pollen and spores distribution was investigated in surface sediments from the shelf and slope 40 2300 m water depth in the offshore area of tokachi plain central eastern hokkaido island the objective of this study was to examine the source transportation and deposition of palynomorphs in marine environments the majority of palynomorphs were transported from the tokachi coastal plain by both strong local winds from the mountain areas during the spring summer and the floods caused by heavy monsoon and typhoon rainfall approximately 10 of all palynomorphs were transported from both southwest and west areas by the wind palynomorph transportation by the oyashio current could not be discriminated because the same vegetation is present in hokkaido and the islands in upper streams of the oyashio current the total grain abundance was dependent on water depth high concentrations were observed at depths of 700 1500 m which is a region associated with high levels of fine silt and clay suggesting that the transportation and deposition of palynomorphs are controlled by their grain sizes this study supported a strong correlation between the distribution of sediments and the concentration of palynomorphs

advection in polar and sub polar environments impacts on high latitude marine ecosystems we compare and contrast the ecological impacts of atmospheric and oceanic circulation patterns on polar and sub polar marine ecosystems circulation patterns differ strikingly between the north and south meridional circulation in the north provides connections between the sub arctic and arctic despite the presence of encircling continental landmasses whereas annular circulation patterns in the south tend to isolate antarctic surface waters from those in the north these differences influence fundamental aspects of the polar ecosystems from the amount thickness and duration of sea ice to the types of organisms and the ecology of zooplankton fish seabirds and marine mammals meridional flows in both the north pacific and the north atlantic oceans transport heat nutrients and plankton northward into the chukchi sea the barents sea and the seas off the west coast of greenland in the north atlantic the advected heat warms the waters of the southern barents sea and with advected nutrients and plankton supports immense biomasses of fish seabirds and marine mammals on the pacific side of the arctic cold waters flowing northward across the northern bering and chukchi seas during winter and spring limit the ability of boreal fish species to take advantage of high seasonal production there southward flow of cold arctic waters into sub arctic regions of the north atlantic occurs mainly through fram strait with less through the barents sea and the canadian archipelago in the pacific the transport of arctic waters and plankton southward through bering strait is minimal in the southern ocean the antarctic circumpolar current and its associated fronts are barriers to the southward dispersal of plankton and pelagic fishes from sub antarctic waters with the consequent evolution of antarctic zooplankton and fish species largely occurring in isolation from those to the north the antarctic circumpolar current also disperses biota throughout the southern ocean and as a result the biota tends to be similar within a given broad latitudinal band south of the southern boundary of the acc there is a large scale divergence that brings nutrient rich water to the surface this divergence along with more localized upwelling regions and deep vertical convection in winter generates elevated nutrient levels throughout the antarctic at the end of austral winter however such elevated nutrient levels do not support elevated phytoplankton productivity through the entire southern ocean as iron concentrations are rapidly removed to limiting levels by spring blooms in deep waters however coastal regions with the upward mixing of iron maintain greatly enhanced rates of production especially in coastal polynyas in these coastal areas elevated primary production supports large biomasses of zooplankton fish seabirds and mammals as climate warming affects these advective processes and their heat content there will likely be major changes in the distribution and abundance of polar biota in particular the biota dependent on sea ice

the effect of fire induced soil hydrophobicity on wind erosion in a semiarid grassland experimental observations and theoretical framework aridland ecosystems are often susceptible to degradation resulting from disturbances like fires and grazing by exposing the soil surface to the erosive action of winds these disturbances contribute to the redistribution of soil nutrients associated with grassland to shrubland conversions and to the formation of a heterogeneous landscape wind erosion maintains the local heterogeneities in nutrient and vegetation distribution in arid landscapes through the removal of nutrient rich soil from the intercanopy areas and the subsequent deposition of soil onto vegetation patches even though wind erosion and disturbances like fires strongly interact with each other and determine vegetation patterns in arid landscapes very few studies have addressed these interactions using soil samples collected after a wildfire event at the cimarron national grasslands in southwestern kansas we demonstrate through a series of wind tunnel experiments laboratory measurements and theoretical analyses how wind erosion can be enhanced by fire induced water repellency results from the wind tunnel experiments show that in semiarid grasslands fires can cause a decrease in the threshold velocity of wind erosion thereby enhancing the post burn erosion of hydrophobic soils further a generalized process based theoretical equation was derived to explain the decrease in threshold friction velocity in water repellent soil for the case of soil particles modeled as asymmetrical cones

threshold for particle entrainment into suspension laboratory observations regarding the limit conditions for particle entrainment into suspension are presented a high speed video system was used to investigate conditions for the entrainment of sediment particles and glass beads lying over a smooth boundary as well as over a rough bed the results extend experimental conditions of previous studies towards finer particle sizes a criterion for the limit of entrainment into suspension is proposed which is a function of the ratio between the flow shear velocity and particle settling velocity observations indicate that particles totally immersed within the viscous sublayer can be entrained into suspension by the flow which contradicts the conclusions of previous researchers a theoretical analysis of the entrainment process within the viscous sublayer based on force balance considerations is used to show that this phenomenon is related to turbulent flow events of high instantaneous values of the reynolds stress in agreement with previous observations in the case of experiments with a rough bed a hiding effect was observed which tends to preclude the entrainment of particles finer than the roughness elements this implies that as the ratio between particle and roughness element sizes becomes smaller progressively higher bed shear stresses are required to entrain particles into suspension on the other hand an overexposure effect was also observed which indicates that a particle moving on a smooth bed is more prone to be entrained than the same particle moving on a bed formed by identical particles

deep currents in the central subarctic pacific ocean abstract sections of closely spaced ctd stations along longs 165 w 175 w and 175 e in combination with 14 month current records from the central longitude define two deep nearly zonal currants with speed increasing upward in the subarctic pacific one flows eastward above the aleutian rise and aleutian trench and appears to be a concentration of geostrophic flow forced by the bottom topography the other flows westward along the aleutian island arc and is the northern boundary current predicted by deep circulation theory both currents reach to the sea surface the boundary current being simply the deep part of the alaskan stream the current records were too few to permit better than rough estimates of volume transports but to the extent that they could be combined with thermal wind calculations they suggest at 175 w 1 a transport of 28 106 m3 s 1 for the alaskan stream of whch 5 106 m3 s 1 was found below 1500 m and 2 a transport of around 20 1o6 m3 s 1 for the eastward jet of wh

on the distribution and separation of crystals in convecting magma abstract fractionation of crystals from magma stands squarely as the central principle of igneous petrology and the critical balance is the competition between crystal settling or rising velocity and magmatic convective velocity a ratio we call s the convective velocity is intimately related to the rate of heat transfer from the system although the theory of sediment distribution in rivers establishes the critical parametric balance and it has been often applied to igneous systems this method turns out to be valid only for small concentrations of crystals and it is not clear if it is accurate for other than turbulent flows where the prandtl number is near unity a generalized theory of particle crystal or bubble behavior is presented scaling of the generalized result shows for the magmatic conditions of small crystallinities small particle reynolds number and newtonian viscosity that the exact distribution of crystals in a convecting magma can be found analytically regardless of the flow field critical retention occurs only for 0 s s 0 for sinking crystals retention is centered in the region of maximum updraft for floating particles retention occurs in regions of downflow which for a simple cellular convective pattern produces a torus shaped retention region against the walls about the midsection of the body for a stack of flattened convective cells which in the crudest sense is analogous to double diffusive convection the zones of retention form depending on the exact flow field either a stack or staggered stack of pillows through the central region crystals settling from top to bottom around this stack take a tortuous path and may exhibit a complex but regular compositional zoning additional effects of fluids possessing a yield strength turbulence particle shape and wall and particle dispersive effects are more qualitatively evaluated for each flow field the amount of retention and the effective settling velocity of all crystals is found as a function of s the critical parameter s controlling retention can be estimated from a parametric representation involving stokes s law and the rayleigh number this shows that some retention probably occurs in all magmas and it increases with approach of the magma to the earth s surface although both crystal settling rate and convection decrease with increasing magmatic viscosity the overall effect is to increase retention decrease s magmas having a viscosity near and beyond about 10 4 poise and chambered in the nearsurface environment should show large degrees of crystal retention retention is however never complete for magmas and the flux of settling crystals leading to differentiation varies as a function of crystallinity this flux or flux probability p f is zero both at the liquidus and the point of maximum packing of crystals which for basalts is about 60 the importance of differentiation is regulated by the amount of time spent in the high crystal flux state and a relative measure of this time is given by the thermal probability p t introduced previously thus the probability of differentiation p d is given by the product p f p t which shows that differentiation must occur over a restricted range of crystallinities from about 20 to 45 for basalts and from about 10 to 30 for rhyolitic magmas the most basic lessons learned here are that the full range of crystallinities is not equally accessible to crystal fractionation and the most fundamental information describing the dynamic state and behavior of magma may well be the distribution of crystal sizes found in lavas

large scale variability in the midlatitude subtropical and subpolar north pacific ocean observations and causes abstract altimetric data from the 8 yr topex poseidon t p mission oct 1992 jul 2000 are used to investigate large scale circulation changes in the three current systems of the midlatitude north pacific ocean the north pacific current npc the alaska gyre and the western subarctic gyre wsg to facilitate the understanding of the observed changes a two layer ocean model was adopted that includes first mode baroclinic rossby wave dynamics and barotropic sverdrup dynamics the npc intensified steadily over the t p period from 1992 to 1998 much of this intensification is due to the persistent sea surface height ssh drop on the northern side of the npc a similar ssh trend is also found in the interior of the alaska gyre both of these ssh changes are shown to be the result of surface wind stress curl forcing accumulated along the baroclinic rossby wave characteristics initiated from the eastern boundary in addition to the interior ssh signals the intensity of the alaska gyre is shown to depend

non stationary entrainment and tunneling eruptions a dynamic link between eruption processes and magma mixing the products of many intermediate arc volcanoes and batholiths manifest compositional complexity with mafic and mixed material occurring early and through out a period of eruption and pluton assembly we present a vesiculation model suggesting that the progressive and repeated vesiculation of volatile rich magmas yields a super linear buoyancy acceleration this style of non stationary entrainment provides a mechanism for compositional reversal the intimate co occurrence of mixed and un mixed magmas and rapid chaotic crystal and melt dispersal under some circumstances entrainment can cease entirely producing eruptions with compositional tunneling where nearly unmixed mafic or newly intruded silicic magma exits first

a local time dependent sverdrup balance in the eastern north pacific ocean direct observations of the dynamic balance between time dependent winds and deep ocean currents are described for the eastern north pacific ocean at 42 n 152 w currents from 150 to 4000 meters below the surface at frequencies from 0 01 to 0 1 cycle per day are significantly correlated with the wind stress curl derived from u s navy operational wind fields the horizontal currents are depth independent below 300 meters and they flow parallel to the potential vorticity gradient derived from the earth9s rotation and the large scale bottom topography these characteristics are expected for such periodic motions with horizontal scales larger than 500 kilometers and represent a generalized sverdrup balance between the atmospheric forcing and the oceanic response

what can we learn from global altimetry hydrography comparisons differences and complementarities between altimeter and hydrographic data are studied to describe the sea level and ocean circulation variations in terms of steric and non steric contributions altimeter sea level anomalies sla and hydrographic dynamic height anomalies dha agree remarkably well they also reveal however systematic large scale differences in several areas of the pacific and indian oceans that are related to a barotropic sverdrup like response of the ocean to wind forcing in addition the use of the two data sets provides a good estimation of the partition between barotropic and baroclinic modes needed for data synthesis or assimilation studies

cold core anticyclonic eddies south of the bussol strait in the northwestern subarctic pacific abstract summer hydrographic surveys from 1993 to 1997 in the area south of the kuril islands in the northwestern subarctic pacific showed the existence of anticyclonic eddies south of the bussol strait at almost the same location but with variable sizes and intensities depending on the year every eddy had a cold low salinity and low potential vorticity core suggesting a strong influence from the okhotsk sea water two formation processes and annual variations were found with satellite data analyses one is the case where eddies are locally formed south of the bussol strait and intensified from summer to fall with the supply of okhotsk sea water as observed in 1993 in the other case kuroshio warm core rings that had translated northeastward are arrested near the bussol strait and amplified with the supply of okhotsk sea water as seen from summer to autumn in 1995 in winter eddies tend to move northeastward with decay the 1992 eddy moved northeastward then northward in winter and was eventually

tidally induced diapycnal mixing in the kuril straits and its role in water transformation and transport a three dimensional nonhydrostatic model experiment 1 baroclinic processes generated by the k1 tidal flow around the kuril straits and their role in the linkage between the okhotsk sea and the north pacific are investigated using a three dimensional nonhydrostatic model large amplitude unsteady lee waves are generated around sill tops all along the kuril island chain and induce significant density inversions from the sea surface down to the 27 6 density layer along with this wave breaking a large flow of energy takes place from the swift tidal flow regions to greater depths as a result of the clockwise propagation of both the topographically trapped waves around the islands and the remaining unsteady lee waves such wave generation and energy exchange eventually cause intense diapycnal mixing over the shallow topographic features and near the bottom leading to a maximum diapycnal diffusivity of over 103 cm2 s 1 even in the deep bussol strait which is thought to be the main exit of the okhotsk sea water considerable mixing corresponding to diapycnal diffusivity values of between 10 50 cm2 s 1 occurs vigorous mixing in the shallow regions produces low potential vorticity pv water in the upper layer and high pv water below accordingly pv fronts are formed along the island chain and sustain instabilities that in turn release baroclinic eddies with low core pv values these features are indicated in recent satellite imagery and in situ observations suggesting that the tide is the controlling factor in the formation of fronts observed in the kuril straits tidally induced mean transport across the straits is estimated to reach 26 sv 1 sv 106 m3 s 1 which is much larger than in the barotropic case however most of the exchanged water tends to circulate around the islands due to the effect of bottom topography whereas eddies pinched off from the tidal fronts carry the exchanged water offshore the amount of eddy driven offshore transport away from the islands reaches 14 sv with roughly half being directed to the north pacific this significant offshore transport spreads the effect of the diapycnal mixing taking place in the straits over wider areas of the north pacific and the okhotsk sea for example the pv values generated in the eddies differ by 30 40 from the ambient water on average whereas sea surface salinity within the eddies is 0 1 psu higher than the surroundings corresponding to the density increase of 0 08 thus the eddy transport provides significant pv and salinity fluxes to both the north pacific and the okhotsk sea hence we infer that a combination of tidally driven processes taking place at the passages leads to the formation of eddies that play a central role in water transport and transformation and are an essential aspect of the physical interplay between the okhotsk sea and the north pacific

laboratory investigations of viscous effects in replenished magma chambers abstract some laboratory experiments are described which investigate the dynamical effects of replenishment of a magma chamber containing high viscosity magma by hotter denser and much more fluid magma in the experiments a layer of hot kno3 solution is emplaced beneath cold glycerine which has a viscosity 3000 times greater less dense fluid is released immediately and continuously from the interface as a result of crystallization in the lower layer and rises as plumes through the overlying glycerine further crystallization occurs in the plumes and the crystals fall out but there is little mixing between the two fluids and a layer of depleted kno3 solution forms at the top the experiments demonstrate that interfacial processes begin to dominate where there are large viscosity differences between adjacent fluid layers as would be the case in a rhyolitic magma chamber replenished by basaltic magma

observations of wind forced deep ocean currents in the north pacific this study examines the atmospheric response of the deep ocean using 200 instrument years of moored current measurements from across the breadth of the mid latitude north pacific we have found evidence of a seasonal modulation in the ocean eddy kinetic energy beneath the thermocline at several locations north of 35 n this modulation is often in phase with the local atmospheric forcing function at frequencies between 0 1 and 0 01 cpd correlations between the local wind stress curl and the deep currents have been found for a few locations the local forced response is parallel to the potential vorticity gradient f h and consistent in amplitude with a local topographic sverdrup balance nonlocal forcing in the form of flow along isolines of potential vorticity has been estimated and it is comparable to the observed flow at some locations but the modeled flow is not correlated with the observations throughout the mid latitude north pacific the bottom slope tends to enhance the effect this suggests that topography narrows the available bandwidth for forced barotropic rossby waves facilitating a quasi steady topographic sverdrup response over most of the basin however the enhanced effect reduces the magnitude of the ocean s response to wind forcing nonlocally forced sverdrup currents flow along isolines of f h are the dominant component but are only of the order of 1 cm s 1 locally forced sverdrup currents flow across isolines of f h are typically of the order of 0 1 cm s 1 rms and are not commonly measured hence these wind forced variations are a background level signal in the mid latitude eddy kinetic energy in a few isolated areas the bottom slope reduces the effect in these regions the local sverdrup response is amplified and has been observed

tracer techniques in aeolian research approaches applications and challenges abstract aeolian processes the entrainment transport and deposition of sediments by wind impacts climate biogeochemical cycles food security environmental quality and human health considering the multitude of interactions between aeolian processes and all the major components of the earth system there is a growing interest in the scientific community to quantify the wind related sediment movement process and redistribution rates at different spatial and temporal scales however this quantification is rather challenging due to the complexities of physical mechanisms involved in aeolian processes and the inherent fundamental differences from the rather well studied processes controlling fluvial erosion traditional techniques such as erosion plots and surveying methods for monitoring wind erosion are capable of quantifying sediment movement on small scales but they have a number of limitations in terms of the representativeness of the data obtained spatial and temporal resolution and the patterns over extended areas and the costs involved the demand for alternative methods of soil loss and sediment redistribution assessment in order to complement and enhance the existing methods has directed attention to use tracing approaches for monitoring rates and spatial patterns of sediment redistribution at various scales a comprehensive synthesis of available information from different scientific disciplines on aeolian tracer techniques their applications and limitations are important in understanding the role of aeolian processes and their interactions with the earths systems in changing climate and management scenarios the objective of this paper is to provide a scientific review of the current tracer approaches in aeolian studies including fallout radionuclides rare earth elements sediment finger printing and soil magnetism as well as giving an introduction of the potential tracers that are in development

on the dynamics of magma mixing by reintrusion implications for pluton assembly processes many plutons have formed by repeated intrusion with complex internal contacts characterized by sharp and diause kinematic and compositional domains we performed numerical experiments of mixing following magma chamber recharge that explicitly considers the fluid dynamics of multiphase mixtures in the limit of zero diausivity of intensive scalar quantities and low stokes number mingling by fluid instability is equivalent to deformation and persistent fluid structures are kinematic attractors three distinct regimes are exemplified and can be described by their multiphase reynolds or grashof number for a reynolds number greater than about 100 an internal intrusive contact will collapse by internal wave breaking and chaotic magma mingling and mixing yield a nearly chamber wide stratification this flow may scour mushy regions at the walls and widely distribute previously crystallized material for reynolds numbers from 10 to 100 the internal wave does not break and the stratification occupies less of the chamber leaving islands of unmixed material for reynolds numbers around 1 internal slumping and folding can occur and is the most likely to be preserved by a mineral fabric internal sub vertical contacts require a high absolute viscosity in the resident magma representing a time break between episodes of reintrusion the shape of perched mafic domains captures the progress of sinking from higher levels into regions of increasing strength and crystallinity 7 2000 elsevier science ltd all rights reserved

scalings for large turbulent flow structures in gravel bed rivers 1 the relations between frequency and duration of large scale turbulent flow structures in gravel bed rivers and the distributions of the time intervals between turbulent events are investigated using flow visualisation and velocity measurements the time of occurrence and the duration and amplitude of large bursting motions were estimated independently from a five minute underwater video and from high resolution velocity time series sampled at 20 hz during 38 minutes at three heights above the bed results from both experiments show that the frequency duration relations of the large scale turbulent flow structures follow a power function with exponents ranging between 1 4 and 1 95 values that are typical of bursting systems e g solar flares the frequency distributions of time intervals between two successive ejections display an exponential tail these findings provide models for simulating sequences of large scale turbulent events in a gravel bed river an important step in linking flow turbulence and sediment transport

expansion and quenching of vesicular magma fragments in plinian eruptions the conditions of pumice generation in plinian eruptions are studied a physical model describes the behavior of gas bubbles in a magma fragment which is carried upward in a volcanic conduit and an atmospheric eruption column the effects of pressure release and cooling are calculated for a range of eruption conditions the magma fragment expands in the conduit and stops expanding soon after leaving the vent when a thin viscous rind forms against the cold mixture of magmatic gas and air this rind prevents further volume changes pumice vesicularity is a function of the decompression rate in the conduit which depends on ascent velocity and fragmentation depth it is also sensitive to the cooling rate in the atmospheric column which depends on vent radius and mass discharge rate different fragments follow different trajectories in the column and are subjected to different cooling rates this generates a range of vesicularities which reflects the eruptive conditions all else being equal pumice vesicularity increases as magma viscosity decreases these predictions are consistent with observations pumices provide quantitative constraints on conduit flow conditions and mass discharge rate these concepts are applied to two plinian eruptions vesicularity values for the bishop tuff long valley caldera require a mass discharge rate between 108 and 109 kg s 1 vesicularity variations during plinian phase 1 of the minoan eruption santorini are explained by the conduit radius increasing from about 30 m to 120 m both cases require large decompression rates in the eruption conduit suggesting that flow pressures were close to lithostatic values

role of winds in estimation of ocean heat storage anomaly using satellite data 1 the heat storage anomaly of the upper ocean can be estimated using altimeter data based on the thermal dynamics equation in this study we analyzed both nonthermal and thermal steric height measured by altimetry and removed nonthermal steric height from altimeter measurements to calculate the heat storage anomaly from thermal steric height alone in the global oceans but with a focus on the pacific ocean after examining nonthermal steric height salinity waves and wind we believe that wind stress is a major component to the change in sea surface height blended topex poseidon and ers 1 2 altimeter 1 1 sea surface height anomaly from january 1993 to october 2000 were used to calculation of the heat storage anomaly in addition we used expendable bathythermograph xbt data to the global oceans to determine a reference heat storage from which the altimeter estimation of the heat storage was compared the wind stress curls from scatterometer data obtained from january 1993 to october 2000 were used for analyzing the wind effects on sea surface height variation the correlation coefficients between heat storage from altimeter data halt and that from the xbt hxbt are larger than 0 6 in the global oceans except in the regions of 20 n in the eastern pacific the eastern tropical pacific the tropical atlantic and the western tropical indian ocean the root mean square rms of the differences halt hxbt has large values in the gulf stream and the kuroshio extension regions as well as the eastern and western tropical pacific and eastern indian ocean the wind induced sea surface height variation exhibits strong annual and interannual cycles so the empirical orthogonal function eof method was employed to extract the cycles the annual cycle has two modes whereas the interannual cycle is characterized by el nino events wind stress can affect the estimation of the heat storage through mechanisms derived from quasi geostrophic and barotropic theory we calculated the correlation coefficient between the differences halt hxbt and wind stress curl the result shows that el nino southern oscillation enso related wind stress curl anomalies are responsible for estimating discrepancy in the regions west of south and north america and tropical oceans the high correlation suggests that in these regions the barotropic and linear theory is the dynamic mechanism underlying the wind effects on heat storage estimation furthermore we focus on baroclinic signal in sea level resulting from ekman upwelling in the tropical oceans the effect of wind forcing has the most important role in sea level change during the 1997 1998 el nino event for instance the heat storage anomaly q due to the strong coastal upwelling off the west coast of peru closely relates to sea surface temperature sst wind forcing remnant sea level height anomaly after removing the contributions of the heat salt and waves to the sea level height and ekman depth dek however the q in the west coast of america and western pacific warm pool areas did not closely relate to sst wind forcing and dek

analysis and simulation of magma mixing processes in 3d abstract magma mixing structures from the lava flow of lesbos greece are analyzed in three dimensions using a technique that starting from the serial sections of rock cubes allows the reconstruction of the spatial distribution of magmas inside rocks two main kinds of coexisting structures are observed i active regions ar in which magmas mix intimately generating wide contact surfaces and ii coherent regions cr of more mafic magma that have a globular shape and do not show large deformations the intensity of mingling is quantified by calculating both the interfacial area ia between interacting magmas and the fractal dimension of the reconstructed structures results show that the fractal dimension is linearly correlated with the logarithm of interfacial area allowing discrimination among different intensities of mingling the process of mingling of magmas is simulated using a three dimensional chaotic dynamical system consisting of stretching and folding processes the intensity of mingling is measured by calculating the interfacial area between interacting magmas and the fractal dimension as for natural magma mixing structures results suggest that as in the natural case the fractal dimension is linearly correlated with the logarithm of the interfacial area allowing to conclude that magma mixing can be regarded as a chaotic process since chemical exchange and physical dispersion of one magma inside another by stretching and folding are closely related we performed coupled numerical simulations of chaotic advection and chemical diffusion in three dimensions our analysis reveals the occurrence in the same system of active mixing regions and coherent regions analogous to those observed in nature we will show that the dynamic processes are able to generate magmas with wide spatial heterogeneity related to the occurrence of magmatic enclaves inside host rocks in both plutonic and volcanic environments

eddies advected by time dependent sverdrup circulation in the western boundary of the subarctic north pacific 1 it has been reported that several eddies frequently exist along the kuril kamchatka trench k k trench hereafter the western boundary of the subarctic north pacific lagged correlation maps of the altimeter derived sea level anomalies slas along the trench indicate that the southern eddies on the whole move northeastward along the k k trench and the northern eddies on the other hand move southwestward by tracking each anticyclonic eddy its propagating velocity along the trench is calculated the time series of the tracked 7 eddies shows similar seasonal variation to those of the first empirical orthogonal function eof of the sla maps and to those of the sverdrup transport at 40 n in addition when more than two eddies remotely exist in the studied area they show coherent moving patterns these results suggest that the eddies in the western boundary region of the subarctic north pacific are advected by the time dependent wind driven current

chaotic advection fractals and diffusion during mixing of magmas evidence from lava flows structures of magma mixing from three different lava flows have been analyzed and the degree of mingling has been quantified by measuring the contact perimeter between magmas and the fractal dimension of structures in each lava flow the values of these parameters suggest that the magma mixing structures were produced by chaotic dynamics induced by stretching and folding processes between the interacting magmas the mingling of magmas has been simulated using a chaotic dynamical system consisting of repeated stretching and folding processes the simulation shows the same patterns of variation of contact perimeter and fractal dimension as those observed in natural structures and indicates that magma interaction processes acted with different intensities in the three lava flows in response to different magmatic interaction regimes since physical dispersion of one magma inside another through stretching and folding processes and chemical exchanges are closely related we performed coupled numerical simulations of chaotic advection and chemical diffusion the results show a good agreement between the computed and natural structures in particular the occurrence in the same system of well and poorly mixed regions it is shown that magma interaction processes are able to generate magmatic masses having wide spatial heterogenity at many length scales this occurrence can account for the presence of magmatic enclaves inside host rocks showing a variable degree of hybridization in both plutonic and volcanic environments

mineral disequilibrium in lavas explained by convective self mixing in open magma chambers characteristic features of many porphyritic andesite and dacite lavas are that they are rich in crystals and display a range of disequilibrium features including reversely zoned crystals resorption surfaces wide ranges of mineral compositions and minerals which are not in equilibrium with the surrounding rock matrix these features are often interpreted as evidence of the mixing of magmas of contrasting composition temperature and origin1 2 here however we propose that such features can also be caused by convection within a magma body with a single composition that is heated from below and cooled from above we describe petrological observations of andesite lava erupted at the soufriere hills volcano montserrat which indicate a heating event and the intermingling of crystals that have very different thermal histories we present experimental data on a representative groundmass composition of this lava which indicate that it is difficult to explain the calcic compositions of plagioclase overgrowth rims and microphenocrysts unless parts of the magma were at temperatures much higher than the inferred average temperature the concept of convective self mixing allows us to explain the occurrence of compositions of minerals that apparently cannot coexist under equilibrium conditions

interannual to decadal variability in the oyashio and its influence on temperature in the subarctic frontal zone an eddy resolving ogcm simulation abstract output of an eddy resolving ogcm simulation is used to investigate mechanisms for interannual to decadal variability in the oyashio and its influence on the subarctic frontal zone in the western north pacific lag correlation analysis reveals that positive anomalies both in basin scale wind stress curl and in local ekman pumping can intensify the southward oyashio almost simultaneously via barotropic and baroclinic rossby wave propagations respectively the oyashio strength can also be influenced by anomalous ekman pumping that is exerted in the western portion of the basin through the baroclinic wave propagation with the lag of 3 yr which appears to arise from a periodicity in the wind field the intensification of the oyashio is accompanied by negative anomalies both in the sea surface temperature and height off of hokkaido island of japan and is followed by their eastward development along the southern branch of the oyashio extension and associated subarctic frontal zone in association with

two phase natural convection implications for crystal settling in magma chambers abstract crystal settling is no longer thought to be the most likely mechanism operating in the formation of layered igneous intrusions the main objection raised against its feasibility is the prediction that crystal settling velocities are likely to be orders of magnitude smaller than convective velocities and that vigorous convection would therefore keep crystals well mixed within the interior of a magma chamber in previous theoretical and numerical investigations of crystal settling no account has been taken of compositional buoyancy gradients created by the interpenetration of crystals and melt this paper includes these effects the results of two dimensional numerical simulations show that parameter regimes exist in which effective crystal settling occurs in infinite prandtl number thermally convecting two phase fluids even for small ratios of settling to convective velocity

crystal settling and in situ crystallization in aqueous solutions and magma chambers abstract laboratory experiments are described in which aqueous solutions of potassium nitrate are cooled from above depending on the viscosity of the solution and the rate at which it is cooled the mechanism of crystallization varies in the least viscous most slowly cooled experiment after an initial period crystals nucleate and grow on pre existing crystals on the floor of the tank driving vigorous compositional convection in more viscous or more rapidly cooled experiments in addition to crystallization on the floor crystals nucleate and grow at the top of the fluid these crystals settle through the solution adding to the crystals on the floor the crystallization mechanism adopted by the laboratory experiments depends on the degree to which the solutions become supersaturated at low cooling rates and viscosities the critical supersaturation for homogeneous nucleation is not exceeded crystals do not form within the fluid and crystallization occurs only on the floor at higher cooling rates and viscosities the critical supersaturation is exceeded in this case crystals are able to form at the top of the fluid and crystal settling operates in addition to crystallization on the floor applying a similar argument to magma chambers it is suggested that in situ crystallization may occur on its own in the most slowly cooled least viscous mafic magma chambers in other chambers crystal settling is expected to accompany in situ crystallization a quantitative assessment of the crystallization of an olivine saturated mafic magma is presented for in situ crystallization to occur alone i e without any superimposed crystal settling in a chamber which is cooled by heat conduction through the country rock supercoolings of between 1 and 20 c must be maintained in the chamber without homogeneous nucleation occurring if crystal settling does occur then the crystals may not form in the thermal boundary layer because although it is the coldest part of the magma it is not necessarily the most supersaturated part because of the effect of pressure on the liquidus