frazil ice formation in an ice shelf water plume 1 we present a model for the growth of frazil ice crystals and their accumulation as marine ice at the base of antarctic ice shelves the model describes the flow of buoyant water upward along the ice shelf base and includes the differential growth of a range of crystal sizes frazil ice formation starts when the rising plume becomes supercooled initially the majority of crystals have a radius of similar to0 3 mm and concentrations are below 0 1 g l depending on the ice shelf slope which controls the plume speed frazil crystals increase in size and number typically crystals up to 1 0 mm in radius are kept in suspension and concentrations reach a maximum of 0 4 g l the frazil ice in suspension decreases the plume density and thus increases the plume speed larger crystals precipitate upward onto the ice shelf base first with smaller crystals following as the plume slows down in this way marine ice is formed at rates of up to 4 m yr in some places consistent with areas of observed basal accumulation on filchner ronne ice shelf the plume continues below the ice shelf as long as it is buoyant if the plume reaches the ice front its rapid rise produces high supercooling and the ice crystals attain a radius of several millimeters before reaching the surface similar ice crystals have been trawled at depth north of antarctic ice shelves but otherwise no observations exist to verify these first predictions of ice crystal sizes and volumes

long term hydroclimatic variability in monsoon shadow zone of western himalaya india tree ring width data of himalayan cedar cedrus deodara roxb g don from 11 homogeneous moisture stressed sites in the monsoon shadow zone of the western himalaya were used to develop a mean chronology extending back to ad 1353 the chronology developed using regional curve standardization method is the first from the himalayan region of india showing centennial scale variations the calibration of ring width chronology with instrumental precipitation data available from stations close to the tree ring sampling sites showed strong direct relationship with march april may june mamj precipitation this strong relationship was used to supplement the instrumental precipitation data back to ad 1410 the precipitation reconstruction showed extended period of drought in fifteenth and sixteenth centuries increasingly pluvial conditions were recorded since eighteenth century with the highest precipitation in the early part of the nineteenth century the decreasing trend in reconstructed precipitation in the last decade of the twentieth century consistent with the instrumental records is associated with the decreasing trend in frequency of western disturbances mamj precipitation over the monsoon shadow zone in the western himalaya is directly associated with the north atlantic oscillation nao and nino3 sst index of el nino southern oscillation enso the leading modes of climate variability influencing climate over large parts of the northern hemisphere however the relationship between enso and mamj precipitation collapsed completely during 1930 1960 the breakdown in this relationship is associated with the warm phase of atlantic multidecadal oscillation amo a spectral analysis of reconstructed mamj precipitation indicates frequencies in the range of the variability associated with modes of nao enso and amo

the influence of eddy viscosity parameterization and turbulence energy closure scheme upon the coupling of tidal and wind induced currents a three dimensional model of the irish sea and the shelf and shelf edge region off the west coast of scotland is used to examine the interaction of wind induced surface currents and m 2 tidal currents which can lead to an increased near surface m 4 tidal current in the region calculations are performed using uniform southerly and westerly wind stresses with vertical eddy viscosity computed using either a simple flow dependent form of viscosity or one related to the flow and surface wind stress or derived using a two equation turbulence model resulting m 4 tidal distributions computed with the various viscosity formulations are compared with each other the spatial distribution the m 4 tidal current in the case of the flow dependent viscosity shows a significant enhancement of the surface m 4 tide due to non linear coupling between the surface shear and the tidally dependent viscosity in deep water this is the dominant mechanism giving rise to an enhancement in near surface m 4 current in shallow water however where other non linear processes are important in generating the m 4 tide namely changes in water depth and friction these are significant as well as the non linear surface shear effect in changing the m 4 tidal distribution however when an eddy viscosity formulation depending upon flow and surface wind stress is used the non linear coupling mechanism producing an enhanced m 4 tidal surface current is reduced and no increase in m 4 surface current occurs calculations with the two equation turbulence model do not produce an increase in the near surface m 4 tide as the near surface viscosity in this model is determined principally by the wind stress rather than the tidal current some conclusions concerned with developing a simple eddy viscosity model having similar characteristics to the turbulence energy model and experimental data sets for validation are considered at the end of the paper

calculating tidal current profiles from vertically integrated models near the critical latitude in the barents sea the method of extracting current profiles from vertically integrated hydrodynamic models is extended to incorporate more general boundary conditions and the consistency of the method is investigated using this method the tidal current profiles for semidiurnal and diurnal constituents are studied in high latitudes near the critical latitude where the coriolis frequency equals the tidal frequency for the semidiurnal tide the current profiles are computed at stations in the barents sea where current measurements exist at up to six different depths the observation stations are located close to the critical latitude for the largest semidiurnal constituents and the current profiles are therefore sensitive to variations of magnitude and vertical distribution of the eddy viscosity at this latitude the current is strongly depth dependent and in deep water the tidal ellipse changes direction of rotation near the seabed at four of the stations there are under ice measurements and the effects of an ice covered ocean upon the tidal current profiles are also investigated

semidiurnal tides on the laptev sea shelf with implications for shear and vertical mixing the arctic continental shelf seas hold a globally significant source of freshwater that impacts arctic ocean stratification circulation and climate this freshwater can be injected below the surface mixed layer by intense turbulent kinetic energy dissipation events as resolved by laptev sea microstructure observations the tides provide a major source of energy that can be dissipated and hence drive diapycnal mixing in the laptev sea multiyear adcp mooring records from locations across the shelf reveal that semidiurnal tides are dominated by them2 and s2 constituents with the largest amplitudes on the outer shelf throughoutmost of the shelf tides are clockwise polarized and sheared by stratification as characteristic near the m2 critical latitude interannual variations of the tidal and shear structures on the inner shelf aremainly determined by the stratification setting lena river freshwater plume in all locations m2 tides are enhanced under sea ice and therefore changes in the seasonal ice cover may lead to changes in tides and water column structure the main conclusions of this study are that i tides play a comparatively greater role year round on the outer shelf relative to the inner shelf ii a sea ice reduction will overall decrease the predictability of the currents especially on the inner shelf and iii the freshwater distribution directly impacts diapycnal mixing by setting the vertical tidal structure these combined effects imply that future sea ice loss will increase the variability and vertical mixing of freshwater particularly on the inner shelf where the lena river first enters the laptev sea

spring temperatures in the far western nepal himalaya since ad 1640 reconstructed from picea smithiana tree ring widths we developed a new 422 year long tree ring width chronology spanning ad 1591 2012 from picea smithiana wall boiss in khaptad national park which is located in the far western nepalese himalaya seasonal correlation analysis revealed significant indirect relationship with spring temperature and lead to the reconstruction of march may average temperature for the past 373 years ad 1640 2012 the reconstruction was found significant based on validation statistics commonly used in tree ring based climate reconstruction furthermore it was validated through spatial correlation with gridded temperature data this temperature reconstruction identified several periods of warming and cooling the reconstruction did not show the significant pattern of cooling during the little ice age but there were few cold episodes recorded the spring temperature revealed relationship with different sea surface temperature index over the equatorial pacific ocean which showed linkages with climatic variability in a global scale

simulations of ice ocean dynamics in the weddell sea 2 interannual variability 1985 1993 investigations of sea ice ocean interaction on the continental shelf in the southwestern weddell sea reveal a strong correlation between fluctuations of atmospheric forcing and the variability of sea ice formation anomalies of meridional wind stress in the inner weddell sea are consistent with the phase of the antarctic circumpolar wave acw positive anomalies of northward wind stress cause an increase of sea ice export in the same and of sea ice formation in the following year leading to an increased production of high salinity shelf water driven by a varying zonal density distribution over the continental shelf the circulation in the filchner ronne ice shelf cavity fluctuates between two modes each of which features a characteristic distribution of basal freezing and melting regions thus signals of interannual atmospheric variability propagate into the deep ocean and the sub ice shelf cavities

warm season temperatures since 1600 bc reconstructed from tasmanian tree rings and their relationship to large scale sea surface temperature anomalies we describe an improved tree ring reconstruction of mean warm season november april temperatures for tasmania from huon pine this record extends back to 1600 bc and is based on a tree ring chronology that was processed to retain as much low frequency variance as possible the resulting reconstruction explains 46 6 of the variance and verifies significantly when compared to withheld instrumental data cross spectral analysis of actual and estimated temperatures over the 1886 1991 common period indicates that most of the unexplained variance is at periods 12 years the squared coherency ranges between 0 6 0 8 and the cross spectral gain indicates that the amplitude of the reconstruction is a nearly unbiased estimate of the true temperature amplitude therefore this reconstruction should be especially useful for studying multi decadal temperature variability in the tasmanian sector of the southern hemisphere over the past 3592 years to this end we examined the time evolution of low frequency temperature amplitude fluctuations and found evidence for a 35 amplitude reduction after ad 100 that persisted until about ad 1900 since that time the low frequency temperature amplitude has systematically increased we also show how this reconstruction is related to large scale sea surface temperatures sst in the indian ocean and eastward to the dateline pointwise correlations between the tasmanian record and ssts reveal a relationship that extends across the southern indian ocean and towards the arabian sea this pattern is largely determined by inter decadal temperature variability with correlations in this 10 year bandwidth commonly exceeding 0 6 over most of the southern indian and southwestern pacific sectors a rotated empirical orthogonal function analysis reveals that the pattern of pointwise correlations found between the temperature reconstruction and ssts is largely explained by the linear combination of three orthogonal modes of sst variability

the effects of tides on the water mass mixing and sea ice in the arctic ocean in this study we use a novel pan arctic sea ice ocean coupled model to examine the effects of tides on sea ice and the mixing of water masses two 30 year simulations were performed one with explicitly resolved tides and the other without any tidal dynamics we find that the tides are responsible for a 15 reduction in the volume of sea ice during the last decade and a redistribution of salinity with surface salinity in the case with tides being on average 1 0 1 8 practical salinity units psu higher than without tides the ice volume trend in the two simulations also differs 2 09 103 km3 decade without tides and 2 49 103 km3 decade with tides the latter being closer to the trend of 2 58 103 km3 decade in the piomas model which assimilates sst and ice concentration the three following mechanisms of tidal interaction appear to be significant a strong shear stresses generated by the baroclinic clockwise rotating component of tidal currents in the interior waters b thicker subsurface ice ocean and bottom boundary layers and c intensification of quasi steady vertical motions of isopycnals by 50 through enhanced bottom ekman pumping and stretching of relative vorticity over rough bottom topography the combination of these effects leads to entrainment of warm atlantic waters into the colder and fresher surface waters supporting the melting of the overlying ice

modeling tidal current profiles and vertical mixing beneath filchner ronne ice shelf antarctica abstract one of the warmest water masses beneath filchner ronne ice shelf fris is dense high salinity shelf water hssw that flows into the sub ice shelf cavity from the ice front and occupies the lower portion of the water column a one dimensional turbulence closure ocean model has been applied to this high latitude sub ice shelf environment to demonstrate that tidal currents mix hssw vertically through the water column and cause melting at the bottom of the ice shelf significantly fris lies near the critical latitude for the semidiurnal tide where the coriolis frequency equals the tidal frequency resulting in a strongly depth dependent tidal current and thick boundary layers using the model the effect of the critical latitude stratification and the polarization of the tidal current ellipse on boundary layer structure and subsequent vertical mixing are examined the model shows that stratification significantly affects how the shape of the tidal current ellipse varies with depth and that both

on formulating two dimensional vertically integrated hydrodynamic numerical models with an enhanced representation of bed stress a convolution method is developed for computing the bottom stress in a vertically integrated hydrodynamic numerical model by this means the bottom stress is no longer related to the depth mean current as in a conventional vertically integrated model and an enhanced representation of the bottom stress is possible an enhanced vertically integrated model consequently the enhanced model can reproduce phase lags and differences in direction between bed stress and depth mean current which cannot be taken into account in conventional vertically integrated models a linear or quadratic frictional formulation can be used with the method idealized calculations of wind induced flow in a rectangular basin show that the bed stress computed by the convolution method is in excellent agreement with that derived using a full three dimensional model however significant differences in the bed stress between the three dimensional and conventional two dimensional model are evident also in this paper a method is developed for extracting current profiles from vertically integrated models current profiles extracted from the enhanced two dimensional model for a range of frictional effects are found to be in good agreement with those computed using a full three dimensional model

drought reconstructions for the continental united states abstract the development of a 2 lat 3 long grid of summer drought reconstructions for the continental united states estimated from a dense network of annual tree ring chronologies is described the drought metric used is the palmer drought severity index pdsi the number of grid points is 154 and the reconstructions cover the common period 1700 1978 in producing this grid an automated gridpoint regression method called point by point regression was developed and tested in so doing a near optimal global solution was found for its implementation the reconstructions have been thoroughly tested for validity using pdsi data not used in regression modeling in general most of the gridpoint estimates of drought pass the verification tests used in addition the spatial features of drought in the united states have been faithfully recorded in the reconstructions even though the method of reconstruction is not explicitly spatial in its design the drought reconstructions show that the 1930s dust bow

transform marginal plateaus abstract numerous submarine plateaus form highstanding bathymetric highs at continent to ocean transitions due to their proximity to continents they have been frequently labelled marginal plateaus although this term has not been clearly defined or associated with a specific geology or geodynamic process until now these elevations have been interpreted as submerged thinned continental fragments detached from continents basaltic buildups formed by hotspots volcanic margins or oceanic plateaus many of these plateaus formed at transform margins connecting oceanic basins of contrasted ages we propose for the first time to define and review a class of marginal plateaus related to a specific tectonic setting transform marginal plateaus tmps based on a compilation of 20 tmps around the world we show that most of them have a polyphased history and have undergone at least one major volcanic phase our review highlights in particular a hitherto unrecognized close link between hotspots volcanic activity and transform margins we also propose that due to their polyphased history tmps may contain several successive basins and overlooked long lived sedimentary archives we finally highlight that because these tmps were transform plate boundaries perpendicular or oblique to surrounding rifts many of them were close to last contact points during final continental breakup and may have formed land bridges or bathymetric highs between continents therefore we discuss broader scientific issues such as the interest of tmps in recording and studying the onset and variations of oceanic currents or past biodiversity growth bio connectivity and lineage evolution

measurements of ice thickness and seabed topography under the fimbul ice shelf dronning maud land antarctica 1 this paper presents results from seismic measurements of the ice and water column thickness of the fimbul ice shelf in the northeastern weddell sea seismic reflection measurements were conducted at 183 stations covering most of the ice shelf seismic velocities in the ice were derived from refraction measurements at 12 stations distributed evenly across the area as well as from temperature and density data from the fimbul ice shelf velocities in the water were derived from temperature and salinity data from beneath the fimbul ice shelf ice thicknesses were found to vary between 160 m and 550 m with uncertainties up to 10 m water column thicknesses up to 900 m were found within the central ice shelf cavity and values exceed 2000 m where the ice shelf overhangs the continental slope uncertainties in water column thickness are estimated to be 60 m and are dominated by the uncertainties in the shape of the seabed ice draft and seabed elevation was derived from ice and water column thickness assuming hydrostatic pressure the resulting map of seabed elevation and water column thickness suggests that the strong westward flowing coastal current will be steered under the ice shelf and thus drive a sub ice shelf flow warm deep water does not have direct access to the ice shelf cavity while relatively cold coastal waters shallower than 500 m will interact closely with the fimbul ice shelf

infragravity velocity profiles in the surf zone we present a theoretical solution for the vertical structure of the velocity profiles in infragravity waves the solution predicts that while the velocity without local forcing of the infragravity waves does not vary significantly with the vertical coordinate the velocity with local forcing of the infragravity waves has a substantial vertical structure

fennoscandian summers from ad 500 temperature changes on short and long timescales quantitative estimates of 1480 years of summer temperatures in northern fennoscandia have previously been derived from continuous treering records from northern sweden here we show the results of spectral analyses of these data only a few peaks in the spectra are consistently significant when the data are analyzed over a number of sub periods relatively timestable peaks are apparent at periods of 2 1 2 5 3 1 3 6 4 8 32 33 and for a range between 55 100 years these results offer no strong evidence for solar related forcing of summer temperatures in these regions our previously published reconstruction was limited in its ability to represent long timescale temperature change because of the method used to standardize the original tree ring data here we employ an alternative standardization technique which enables us to capture temperature change on longer timescales considerable variance is now reconstructed on timescales of several centuries in comparison with modern normals 1951 70 generally extended periods when cool conditions prevailed prior to the start of the instrumental record include 500 700 790 870 1110 1150 1190 1360 1570 1750 a d with the most significant cold troughs centred on about 660 800 1140 1580 1620 and 1640 predominantly warm conditions occurred in 720 790 870 1110 and 1360 1570 with peaks of warmth around 750 930 990 1060 1090 1160 1410 1430 1760 and 1820

effect of critical latitude and seasonal stratification on tidal current profiles along ronne ice front antarctica 1 the ice front region of ronne ice shelf lies near the critical latitude of the semidiurnal m2 tide the principal tidal constituent in the southern weddell sea here the coriolis frequency almost equals the m2 tidal frequency resulting in a strong dependence of the m2 tidal currents on depth and stratification and a boundary layer that can occupy the entire water column using data from four long term moorings along ronne ice front we confirm the presence of strongly depth dependent semidiurnal tidal currents and their sensitivity to changes in stratification the time series show dramatic seasonal changes in tidal current profiles and significant interannual variability during periods of stratification the amplitude of the semidiurnal tides in the mid water column shows a twofold increase and despite being several kilometers offshore from the ice front the tidal currents clearly show a second boundary layer originating from the adjacent ice shelf base together these two boundary layers occupy most of the water column up to 600 m deep until intense sea ice formation and the production of high salinity shelf water erodes the vertical stratification during winter when homogeneous conditions prevail a single bottom boundary layer occupies the entire water column at some locations this strong seasonality and sensitivity of the m2 tidal current to stratification highlights the difficulties of interpreting current data from short term moorings while demonstrating that it is the best indicator for characterizing changes in stratification after direct observations of density variations

elemental and isotopic chloride geochemistry and fluid flow in the nankai trough 1 the first transect of pore fluid cl profiles across the deformation front of an accretionary prism and underthrust section nankai trough and the first cl isotopic profile in this environment are presented these demonstrate that there is channelized horizontal episodic flow through most of the section arcward of the deformation front and in the lowermost section seaward of the deformation front in the underthrust sediments channels appear to be continuous fluid velocities within the channels based on cl gradients are 13 5cm year the near balance of depth integrated flow and the subduction of pore fluid indicates that flow episodes are frequent 37cl values are lower than seawater throughout the section averaging 6 1 per mil this demonstrates fluid mineral exchange of cl and suggests that subducted solids carry enriched 37cl that is efficiently recycled from deeper levels in the subduction zone back into seawater and may be responsible for the seawater mantle 37cl fractionation

spring precipitation variations over the western himalaya india since a d 1731 as deduced from tree rings 1 spring precipitation representative of regional scale features was reconstructed since a d 1731 using 15 site ring width chronologies of himalayan cedar cedrus deodara roxb ex lambert g don prepared from distantly located moisture stressed sites in the western himalayan region this is so far the strongest tree ring based precipitation reconstruction in terms of variance explained in the calibration model a d 1897 1986 from the western himalayan region the twentieth century experienced the driest and wettest years in the whole reconstructed series the 10 and 20 year means also indicate extreme precipitation periods in the twentieth century the increasing precipitation trend noticed in the reconstructed data of the late twentieth century closely matches with instrumental data

on extracting tidal current profiles from vertically integrated two dimensional hydrodynamic models a numerically accurate and computationally efficient method is developed for extracting tidal current profiles from vertically integrated two dimensional models the method can incorporate an arbitrary profile of eddy viscosity and determines tidal current profiles satisfying a no slip condition at the sea bed comparisons with observations and current profiles computed with full three dimensional models confirm the accuracy of the method bottom boundary layer thicknesses determined from these current profiles clearly show regions of the european continental shelf where the bottom boundary layer extends to the sea surface the boundary between these regions and other areas where the bottom layer is less than the water depth corresponds quite closely to the known position of tidal fronts

how enso impacts precipitation in southwest central asia 1 a linkage between enso and the hydroclimatic variability of the southwest central asia region swca is established through observational analysis of precipitation moisture flux and sea level pressure data with further support from an atmospheric model of intermediate complexity enhanced precipitation in swca during warm enso events results from an anomalous southwesterly moisture flux coming from the arabian sea and tropical africa which is generated along the northwestern flank of the high pressure anomaly over the indian and western pacific oceans part of the canonical enso sea saw pressure anomalies the enso impact on swca precipitation is found to be greatest in the transition seasons of autumn and spring but the dynamical impact on pressure and circulation persists throughout the year this connection was particularly strong in recent decades model sensitivity experiments further show that this is driven primarily by tropical pacific sst anomalies and associated large scale sea level pressure changes while the indian ocean sst has opposite effects

a tree ring based reconstruction of the atlantic multidecadal oscillation since 1567 a d 1 we present a tree ring based reconstruction of the atlantic multidecadal oscillation amo which demonstrates that strong low frequency 60 100 yr variability in basin wide 0 70 n sea surface temperatures ssts has been a consistent feature of north atlantic climate for the past five centuries intervention analysis of reconstructed amo indicates that 20th century modes were similar to those in the preceding 350 yr and wavelet spectra show robust multidecadal oscillations throughout the reconstruction though the exact relationships between low frequency sst modes higher frequency 7 25 yr atmospheric modes e g north atlantic oscillation arctic oscillation and terrestrial climates must still be resolved our results confirm that the amo should be considered in assessments of past and future northern hemisphere climates

assessment of solute and suspended sediments acquisition processes in the bara shigri glacier meltwater western himalaya india various physico chemical parameters of meltwater samples from bara shigri glacier collected during 2012 2013 were analysed to understand the dissolved ion chemistry and solute acquisition processes regulating major ion chemistry of the study area ionic dominance of anions followed the trend as hco3 so4 2 cl no3 whereas ionic dominancy of cations varied as ca2 mg2 k na for both the years high share of ca mg in the total cations and also dominancy of ca mg over na k for both the years demonstrate that solute acquisition processes in the meltwater of bara shigri glacier are mainly governed by the weathering of carbonates the piper plot identified ca hco3 as the dominant water type followed by caso4 type of water in the study area the average value of partial pressure of carbon dioxide pco2 for meltwater of the bara shigri glacier was 10 2 6 atm in 2012 and 10 2 3 atm in 2013 and were higher than the pco2 value of atmosphere 10 3 5 atm it indicates that the meltwater is in disequilibrium with respect to the atmosphere contents of suspended sediment in the meltwater were 1432 mg l in july and 596 mg l in september 2012 whereas in 2013 suspended sediment contents were 1093 mg l in august and 425 mg l in september following discharge pattern of the bara shigri glacier we found that bara shigri and gangotri glaciers demonstrate the higher rate of regional melting

application of a three dimensional turbulence energy model to the determination of tidal currents on the northwest european shelf a three dimensional turbulence energy tidal model employing a sigma coordinate system through the vertical with a logarithmic type transformation to enhance near bed resolution is used to examine m2 tidal currents on the european continental shelf a no slip bottom boundary condition is applied in the model and vertical eddy viscosity is computed from a turbulence energy closure scheme comparisons of observed and computed current profiles determined using the present model and an earlier model employing a spectral representation davies 1986 in the vertical and a slip bottom boundary condition are made in this spectral model a simple relationship between eddy viscosity and depth mean current was employed these comparisons of current profile suggest that above the near bed layer the spectral model can reproduce tidal currents with a comparable accuracy to that of the present turbulence energy model however in the near bed region the turbulence energy model is significantly more accurate computed spatial distributions of current magnitude turbulence energy intensity and eddy viscosity show similar distributions over the model region suggesting that a relationship between eddy viscosity and current intensity the form used in the spectral model is a valid alternative to using a turbulence energy model turbulence energy intensity in particular exhibits significant spatial variations both horizontally and vertically with surface contours of turbulence corresponding to known positions of tidal fronts

observations of turbulent mixing and hydrography in the marginal ice zone of the barents sea 1 measurements of hydrography currents microstructure shear and temperature were made at ice drift stations in the marginal ice zone miz of the northern barents sea highly variable mixing regimes were observed within and below the pycnocline elevated turbulent dissipation 5 15 10 7 w kg 1 was associated with strong vertical shear between the surface layer and the subsurface currents as well as strong tidal flow over shallow topography dissipation in the pycnocline was enhanced at stations with strong wind forcing during drifts under relatively calm wind and away from strong fronts and abrupt topography station mean dissipation values were up to a factor 50 lower and double diffusion contributed significantly to the vertical heat flux where hydrography favored diffusive layering independent measures of turbulent length scale from density overturns compared well with those inferred from the dissipation measurements the variability of dissipation was better captured using a scaling by shear suggested for shelves rather than shear variance models appropriate to the deep open ocean sufficiently resolved patches of enhanced temperature microstructure used in combination with dissipation measurements suggest mixing efficiency of rf 0 2 for patches stable to double diffusion comparable to the conventional upper bound of rf 0 17 mixing efficiency for double diffusive convection favorable cases is found to be significantly larger rf 0 36 water mass modification and fluxes of nutrients and dissolved carbon were found to have large local variability in accordance with the observed variability of vertical mixing in the miz

a coupled ice ocean model of upwelling in the marginal ice zone a dynamical coupled ice ocean numerical model for the marginal ice zone miz is suggested and used to study upwelling dynamics in the miz the nonlinear sea ice model has a variable ice concentration and includes internal ice stress the model is forced by stresses on the air ocean and air ice surfaces the main coupling between the ice and the ocean is in the form of an interfacial stress on the ice ocean interface the ocean model is a linear reduced gravity model the wind stress exerted by the atmosphere on the ocean is proportional to the fraction of open water while the interfacial stress ice ocean is proportional to the concentration of ice a new mechanism for ice edge upwelling is suggested based on a geostrophic equilibrium solution for the sea ice medium the upwelling reported in previous models invoking a stationary ice cover is shown to be replaced by a weak downwelling due to the ice motion most of the upwelling dynamics can be understood by analysis of the divergence of the across ice edge upper ocean transport on the basis of numerical model an analytical model is suggested that reproduces most of the upwelling dynamics of the more complex numerical model

review of recent developments in tidal hydrodynamic modeling i spectral models in this paper we present a brief overview with a comprehensive set of references to recently published papers for detail of a range of techniques used in tidal hydrodynamic modeling and recent progress in the field although the paper aims to introduce the topic to someone new to the area the main emphasis is on new developments in near coastal shallow sea tidal modeling and consequently we concentrate on three dimensional modeling which has progressed significantly in recent years the paper gives a brief account of methods used to discretize the hydrodynamic equations in the horizontal namely finite difference finite element and boundary fitted coordinates and through time the representation of tidal current structure in a three dimensional model using a spectral method in the vertical is also described in this method the subgrid scale vertical diffusion of momentum which has a major influence on tidal current profiles is parameterized using a flow dependent eddy viscosity recent work on

model simulations of the tides in the barents sea a large scale numerical model covering the nordic seas and the arctic ocean with 25 12 5 km grid resolution has been applied to study the tides in the barents sea tidal charts for elevation and phase are presented for the four tidal constituents m2 s2 n2 and k1 computed harmonic constants for elevation and current have been compared with observations from 46 coastal and pelagic tidal stations the agreement between model and field data is good for most stations with an overall standard deviation of 2 5 cm for amplitude 18 30 for phase and 1 3 cm s for current speed calculated tidal residual currents show anticyclonic eddy circulation over the svalbard bank and around bear island and hopen particle trajectories and streaklines due to the tidal flow over svalbardbanken have been calculated and the computed streaklines are found to agree well with observed rifts in the ice cover due to stranded icebergs

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

high frequency ice motion and divergence in the weddell sea we describe the spatial variability of high frequency ice velocity in the weddell sea using satellite tracked ice mounted buoys ice motion is analyzed separately for diurnal 1 36 1 18 cph and semidiurnal 1 18 1 6 cph bands ice motion in both bands is caused by a combination of ocean tidal currents and wind stress monthly mean diurnal band ice speeds over the deep basin range from 2 to 4 cm s 1 depending on wind stress variance and ice concentration cice higher speeds 10 cm s 1 are found in the semidiurnal band in regions of low cice notably the northern weddell sea where the ice velocity is dominated by the inertial response to wind stress variations monthly mean tidal band ice speeds over the continental slope and shelves often exceed 10 cm s 1 we use comparisons between buoy velocities moored current meter data and an ocean tidal model to demonstrate that ice motion is frequently a good indicator of ocean tidal currents in strongly tidal regions the standard deviation of the divergence of ocean tidal currents estimated from an ocean only tidal model is small 0 1 10 6 s 1 over most of the weddell sea but has values of 1 5 10 6 s 1 along the ronne ice front and the continental shelf break high frequency ice divergence is dominated by ice response to wind stress rather than by tides except along the shelf break and ice fronts in these tidally dominated regions the periodic divergence maintains a mean lead open water area of 2 5 this increased lead fraction implies an increase in area averaged winter ocean to atmosphere heat exchange rate of 4 10 w m 2 and an increase in salt flux into the upper ocean as new ice forms in the leads

forcing of the asian monsoon on the tibetan plateau evidence from high resolution ice core and tropical coral records 1 climatic influences on snow accumulation across the tibetan plateau are examined using records of net snow accumulation an and oxygen isotopic ratios 18o since 1801 from two ice cores from opposite sides of the plateau from 1880 to the 1990s summer monsoon precipitation has been a significant component of the annual accumulation on the dasuopu glacier in the himalayas but during the latter part of the little ice age 1810 to 1880 total an was 30 higher than the summer monsoon amounts in northern india this was possibly the result of increased early winter snowfall as westerly low pressure systems linked to the north atlantic pushed farther east along the himalayas than they normally do today the decades of high accumulation and the colder temperatures allowed excess snow and ice to persist late into each year which may have weakened the subsequent asian summer monsoon consequently precipitation in the northeast tibetan plateau where the dunde ice cap is located may have been affected primarily by eurasian continental processes rather than tropical meteorology during this time since the onset of the recent warming over the last century the south asian summer monsoon intensified and influenced summer climate farther to the north and west and expressions of tropical pacific and indian oceanic atmospheric processes are noticeable in the dunde net accumulation record the dunde and dasuopu glaciers which are located on the northern and southern rims of the tibetan plateau were situated in regions of environmental transition as the northern hemisphere climate shifted from a neoglacial to a warming climate mode which is something to consider when interpreting the longer ice core climate records