turbulent mixing near the yermak plateau during the coordinated eastern arctic experiment during the ice camp component of the coordinated eastern arctic experiment cearex in march april 1989 1500 profiles of temperature conductivity and velocity shear microstructure were obtained near the yermak plateau the dominant signal in isopycnal displacements was the diurnal variability near the plateau consistent with the enhanced diurnal currents found in this region previously from the fram iii and fram iv ice camps the dissipation rate of turbulent kinetic energy e reached maximum values of about 10 6 w kg 1 in two distinct regions the surface mixing layer and the pycnocline between 120 and 220 m there was a significant component of diurnal variability in e in each region in the surface layer e was proportional to the cube of the ice relative current speed at 30 m below the ice and it decayed approximately exponentially with increasing depth major mixing events in the pycnocline were correlated with large amplitude short duration isopycnal displacements the lowest dissipation rates were recorded over the deep nansen basin north of the plateau and in the subsurface core of a submesoscale baroclinic eddy in northern fram strait the time averaged vertical eddy diffusivity near the slope of the plateau was about 2 5 10 4 m2 s 1 in the pycnocline above the atlantic layer implying an upward heat flux of 25 w m 2 although only a small fraction of this heat reached the base of the mixed layer the results confirm that current interactions with steep topography are critical to the modification of atlantic water in the eastern arctic ocean

inertial currents in the beaufort sea observations of response to wind and shear doppler sonar observations from the arctic internal waves experiment and arctic leads experiment in the beaufort sea are used to examine currents below the ice during spring conditions following two strong wind events the dominant fine scale current consists of both downward and upward propagating near inertial internal waves the downward propagating waves are most evident above 100 m depth while the upward waves are most energetic below this depth the appearance of these waves coincides in time and depth with a westward subinertial current following the winds with maximum speeds of 0 05 m s 1 at 100 m depth simple ray simulations show that the observed subinertial shear can significantly refract near inertial waves with length scales similar to those observed in particular waves that propagate both in the direction of the current and toward the depth of maximum current are enhanced these simulations suggest that the observed near inertial wave enhancement is due in part to wave shear effects rather than solely to surface forcing

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

on the generation of bottom trapped internal tides abstractthe interaction of the barotropic tide with bottom topography when the tidal frequency is smaller than the coriolis frequency f is examined the resulting waves are called bottom trapped internal tides the energy density associated with these waves is computed using linear wave theory and vertical normal mode decomposition in an ocean of finite depth the global calculation of the modal energy density is performed for the semidiurnal m2 tidal constituent and the two major diurnal tidal constituents k1 and o1 an observationally based decay time scale of 3 days is then used to transform the energy density to energy flux in units of watts per square meter the globally integrated energy fluxes are found to be 1 99 and 1 43 gw for the k1 and o1 tidal constituents respectively for the m2 tidal constituent it is found to be 1 15 gw the pacific ocean is found to be the most energetic basin for the bottom trapped diurnal tides two regional estimates of the bottom trapped energy flux are given for

laboratory experiments on internal solitary waves in ice covered waters internal solitary waves isws propagating in a stably stratified two layer fluid in which the upper boundary condition changes from open water to ice are studied for cases of grease level and nilas ice the isw induced current at the surface is capable of trans porting the ice in the horizontal direction in the level ice case the transport speed of relatively long ice floes non dimensionalised by the wave speed is linearly dependent on the length of the ice floe non dimensionalised by the wave length measures of turbulent kinetic energy dissipation under the ice are comparable to those at the wave density interface moreover in cases where the ice floe protrudes into the pycnocline interaction with the ice edge can cause the isw to break or even be destroyed by the process the results suggest that interaction between isws and sea ice may be an important mechanism for dissipation of isw energy in the arctic ocean

vertical mixing at intermediate depths in the arctic boundary current microstructure and hydrographic observations during september 2007 in the boundary current on the east siberian continental slope document upper ocean stratification and along stream water mass changes a thin warm surface layer overrides a shallow halocline characterized by a 40 m thick temperature minimum layer beginning at 30 m depth below the halocline well defined thermohaline diffusive staircases extended downwards to warm atlantic water intrusions found at 200 800 m depth observed turbulent eddy kinetic energy dissipations are extremely low epsilon 10 6 w m 3 such that double diffusive convection dominates the vertical mixing in the upper ocean the diffusive convection heat fluxes f dc h 1 w m 2 are an order of magnitude too small to account for the observed along stream cooling of the boundary current our results implicate circulation patterns and the influence of shelf waters in the evolution of the boundary current waters

deciphering late devonian early carboniferous p t t path of mylonitized garnet mica schists from prins karls forland svalbard this is the peer reviewed version of the following article ko minska k spear f s majka j faehnrich k manecki m piepjohn k dallmann w k 2020 deciphering late devonian early carboniferous p t t path of mylonitized garnet mica schists from prins karls forland svalbard journal of metamorphic geology which has been published in final form at https doi org 10 1111 jmg 12529 this article may be used for non commercial purposes in accordance with wiley terms and conditions for use of self archived versions

internal tides and turbulence along the 3000 m isobath of the hawaiian ridge full depth velocity and density profiles taken along the 3000 m isobath characterize the semidiurnal internal tide and bottom intensified turbulence along the hawaiian ridge observations reveal baroclinic energy fluxes of 21 5k w m 1 radiating from french frigate shoals 17 2 5 kw m 1 from kauai channel west of oahu and 13 3 5 kw m 1 from west of nihoa island weaker fluxes of 1 4 2k w m 1 radiate from the region near necker island and east of nihoa island observed off ridge energy fluxes generally agree to within a factor of 2 with those produced by a tidally forced numerical model average turbulent diapycnal diffusivity k is 0 5 1 10 4 m 2 s 1 above 2000 m increasing exponentially to 20 10 4 m 2 s 1 near the bottom microstructure values agree well with those inferred from a finescale internal wave based parameterization a linear relationship between the vertically integrated energy flux and vertically integrated turbulent dissipation rate implies that dissipative length scales for the radiating internal tide exceed 1000 km

wind driven mixing at intermediate depths in an ice free arctic ocean recent seasonal arctic ocean sea ice retreat is a major indicator of polar climate change the arctic ocean is generally quiescent with the interior basins characterized by low levels of turbulent mixing at intermediate depths in contrast under conditions of reduced sea ice cover there is evidence of energetic internal waves that have been attributed to increased momentum transfer from the atmosphere to the ocean new measurements made in the canada basin during the unusually ice free and stormy summer of 2012 show previously observed enhancement of internal wave energy associated with ice free conditions however there is no enhancement of mixing at intermediate depths away from significant topography this implies that contrary to expectations of increased wind induced mixing under declining arctic sea ice cover the stratification in the central canada basin continues to suppress turbulent mixing at intermediate depths and to effectively isolate the large atlantic and pacific heat reservoirs from the sea surface

internal wave variability in the beaufort sea during the winter of 1993 1994 1 acoustic doppler current profiler observations were obtained at the sea ice mechanics initiative ice camp as it drifted through the beaufort sea over the winter of 1993 1994 in this paper the variability of the internal wave field is examined initially december 1993 january 1994 the camp drifted westward through the central canada basin 75 n 139 153 w numerous anticyclonic baroclinic eddies were encountered internal wave energy levels averaged 1 25 of the garrett munk gm standard shear variance averaged 1 17 gm during february march 1994 the camp drifted meridionally along 156 w near the northwind ridge reversing direction several times large baroclinic vortices were not detected internal wave energy levels were significantly greater during this period peaking at 1 6 gm shear variance peaked at 1 3 gm the waves were predominantly near inertial resulting from three distinct surface generation events downward vertical energy fluxes ranged from typical values of 0 02 mw m2 to a peak value of 0 15 mw m2 two thirds of the downward flux was associated with waves of vertical scale greater than 55 m the remainder with smaller scale waves upward energy fluxes ranged from 0 02 mw m2 typical to 0 10 mw m2 peak supported almost entirely by the larger scale waves high ice water relative velocities atmospheric storms accompanied by ice deformation appear to be necessary but not sufficient to assure a downward propagating wave generation event the highly variable mesoscale has a significant effect on the near inertial wave field propagation the data suggest that the vertical propagation of near inertial waves is strongly affected by the depth variation of the vertical component of mesoscale vorticity the large beaufort sea vortices appear to have a dual effect on the wave field enhanced vertical propagation speed and decreased energy density is found in the negative vorticity cores propagation into the positive vorticity regions surrounding the cores is inhibited the increase in wave energy experienced as the ice camp left the central beaufort sea is jointly associated with the passage of storms and the absence of large baroclinic vortices over the northwind ridge

tide mediated warming of arctic halocline by atlantic heat fluxes over rough topography atlantic water brings heat to the subsurface arctic ocean pan arctic microstructure measurements of energy dissipation suggest that vertical mixing is substantial over the continental slopes tidally induced and insensitive to sea ice cover

internal waves in the arctic ocean comparison with lower latitude observations abstract a thermistor chain was moored below the pack ice from 50 150 m in the arctic ocean for five days in 1981 oscillations in temperature are attributed to the vertical dispalcement of internal waves the spectral shape of isotherm dispalcement is consistent with the garrett munk model and other internal wave observations but the spectral level is significantly lower other observations from the arctic ocean also exhibit lower internal wave energy when compared with historical data from lower latitudes the lower energy may be related to the unique generation and dissipation mechanisms present in the ice covered arctic ocean significant peaks in vertical coherence occur at 0 81 and 2 6 cph the peak at 2 6 cph coincides approximately with the high frequency spectral cutoff near the local buoyancy frequency this feature has been observed in many other internal wave experiments the coherent oscillations at 0 81 cph exhibit a node in vertical dispalcement at 75 100 m this is consistent with either

four large scale field aligned current systems in the dayside high latitude region a system of four current sheets of large scale field aligned currents facs was discovered in the data set of simultaneous viking and dmsp f7 crossings of the dayside high latitude region this paper reports four examples of this system that were observed in the prenoon sector the flow polarities of facs are upward downward upward and downward from equatorward to poleward the lowest latitude upward current is flowing mostly in the cps precipitation region often overlapping with the bps at its poleward edge and is interpreted as a region 2 current the pair of downward and upward facs in the middle of the structure are collocated with structured electron precipitation the precipitation of high energy 1 kev electrons is more intense in the lower latitude downward current sheet the highest latitude downward flowing current sheet is located in a weak low energy particle precipitation region suggesting that this current is flowing on open field lines simultaneous observations in the postnoon local time sector reveal the standard three sheet structure of facs sometimes described as region 2 region 1 and mantle referred to the midday region 0 currents a high correlation was found between the occurrence of the four fac sheet structure and negative interplanetary magnetic field imf by we discuss the fac structure in terms of three types of convection cells the merging viscous and lobe cells during strongly negative imf by two convection reversals exist in the prenoon sector one is inside the viscous cell and the other is between the viscous cell and the lobe cell this structure of convection flow is supported by the viking electric field and auroral uv image data based on the convection pattern the four fac sheet structure is interpreted as the latitudinal overlap of midday and morning fac systems we suggest that the four current sheet structure is common in a certain prenoon local time sector during strongly negative imf by

a modified law of the wall applied to oceanic bottom boundary layers 1 near the bottom the velocity profile in the bottom boundary layer over the continental shelf exhibits a characteristic law of the wall that is consistent with local estimates of friction velocity from near bottom turbulence measurements farther from the bottom the velocity profile exhibits a deviation from the law of the wall here the velocity gradient continues to decrease with height but at a rate greater than that predicted by the law of thewall with the local friction velocity we argue that the shape of the velocity profile is made consistent with the local friction velocity by the introduction of a new length scale that near the boundary asymptotes to a value that varies linearly from the bottom farther from the boundary this length scale is consistent with the suppression of velocity fluctuations either by stratification in the upper part of the boundary layer or by proximity to the free surface the resultant modified law of the wall provides a good representation of velocity profiles observed over the continental shelf when a local estimate of the friction velocity from coincident turbulence observations is used the modified law ofthe wall is then tested on two very different sets of observations from a shallow tidal channel and from the bottom of the mediterranean outflow plume in both cases it is argued that the observed velocity profile is consistent with the modified law of the wall implicit in the modified law of the wall is a new scaling for turbulent kinetic energy dissipation rate this new scaling diverges from the law of the wall prediction above 0 2d where d is the thickness of the bottom boundary layer and agrees with observed profiles to 0 6d

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

hydrography and microstructure of an arctic cyclonic eddy hydrographic and velocity profiles were made through a small baroclinic cyclonic eddy during the arctic internal wave experiment in the canada basin in april 1985 the maximum measured azimuthal velocity was 0 38 m s 1 at a depth of 115 m with velocities decaying to near zero at 30 and 270 m maximum isopycnal displacements at the closest approach to the eddy s axis were about 40 m the deduced radius of maximum velocity is r0 7 2 km and the total radius is about 13 km kinetic energy dissipation rate e was enhanced within 70 m of the surface throughout the transect and for radius r r0 near 60 m and 180 m the subsurface maxima in e do not correspond to regions of low richardson number but are colocated with locally reduced shear consistent with the observed dissipation rates being merely the remnants of recent more energetic mixing events the time scale for the decay of the eddy based on its total energy and the measured dissipation rates is o 10 years given this large dissipation time scale critical layer absorption of vertically propagating internal wave momentum may be dynamically significant to the eddy s evolution the arctic internal wave experiment aiwex was conducted from an ice camp drifting in the canada basin of the arctic ocean during march may 1985 velocity temperature and conductivity were sampled at fixed depths and profiles of these variables from the surface to below 300 m were made toward the end of the experiment the camp drifted across a small eddy with a total inferred radius see section 3 1 of about 13 km from both the hydrographic data and current meter records the rotation sense parity of the eddy was cyclonic with an azimuthal velocity maximum near 115 m decreasing to approximately zero near 30 m and 270 m small eddies are a common feature of the canada basin being present in about 25 of the hydrographic and current meter profiles during the extensive arctic ice dynamics joint experiment aidjex program in 1975 1976 manley and hunkins 1985 they contain much of the kinetic energy in the depth range 0 250 m and transport significant amounts of anomalous heat salt and nutrients within the canada basin understanding these eddies is therefore essential to modeling the upper ocean in the canada basin manley and hunkins 1985 found that approximately 95 of eddies identified during aidjex were anticyclonic hunkins 1974 documented one cyclonic eddy extending from near the surface to below 200 m from the aidjex pilot program in 1972 manley and hunkins 1985 found three cyclonic eddies during the main aidjex program in 19751976 but two of these were below the atlantic layer core i e below 500 m while the third was very weak d asaro

entrainment induced by near inertial drift of sea ice and its impact on under ice biogeochemical processes in marginal ice zones abstract mooring observation of hydrography hydrodynamics and suspended particles distribution under a drifting sea ice revealed the mixing and entrainment pattern in the upper mixed layer ml of the marginal ice zone the ice floe where the mooring system was installed drifted as near inertial motion with approximately 12 h cycle the mixing pattern induced by this near inertial drift can be divided into two distinct regimes first simple entrainment upward fluxes from the seasonal pycnocline to sea ice water boundary are induced by shear across ml and seasonal pycnocline during the period when ice floes drift toward pack ice the entrainment speed was in the range of 0 25 2 m h 1 which matches well with thickening and thinning of the ml during a near inertial period turbulent wakes on the boundary between sea ice and open water occurred behind the advancing edge of ice in the second regime when ice floes drift toward open ocean the turbulent wakes at the advancing edge of ice are combined with the entrainment caused by near inertial motion which results in a complex mixing pattern of both upward and downward fluxes in the ml the echo intensity observed by the acoustic doppler current profiler and beam attenuation from transmissometer revealed the elevated concentration of suspended particulate materials in the ml which can be direct evidence visualizing the mixing pattern results suggest that the mixing and entrainment found in our study sustain particulate matters in suspension within upper ml for a few months this may provide a potential mechanism to sustain abundant organic particulates in the ml and upper pycnocline for months after under ice bloom under strong wind events like storms the entrainment induced by near inertial motion may also get enhanced which causes elevated supply of nutrients from the deeper permanent pycnocline to the ml

mixing rates and vertical heat fluxes north of svalbard from arctic winter to spring mixing and heat flux rates collected in the eurasian basin north of svalbard during the n ice2015 drift expedition are presented the observations cover the deep nansen basin the svalbard continental slope and the shallow yermak plateau from winter to summer mean quiescent winter heat flux values in the nansen basin are 2 w m 2 at the ice ocean interface 3 w m 2 in the pycnocline and 1 w m 2 below the pycnocline large heat fluxes exceeding 300 w m 2 are observed in the late spring close to the surface over the yermak plateau the data consisting of 588 microstructure profiles and 50 days of high resolution under ice turbulence measurements are used to quantify the impact of several forcing factors on turbulent dissipation and heat flux rates wind forcing increases turbulent dissipation seven times in the upper 50 m and doubles heat fluxes at the ice ocean interface the presence of warm atlantic water close to the surface increases the temperature gradient in the water column leading to enhanced heat flux rates within the pycnocline steep topography consistently enhances dissipation rates by a factor of four and episodically increases heat flux at depth it is however the combination of storms and shallow atlantic water that leads to the highest heat flux rates observed ice ocean interface heat fluxes average 100 w m 2 during peak events and are associated with rapid basal sea ice melt reaching 25 cm d

reduced mixing from the breaking of internal waves in equatorial waters in the oceans heat salt and nutrients are redistributed much more easily within water masses of uniform density than across surfaces separating waters of different densities but the magnitude and distribution of mixing across density surfaces are also important for the earth s climate as well as the concentrations of organisms most of this mixing occurs where internal waves break overturning the density stratification of the ocean and creating patches of turbulence predictions of the rate at which internal waves dissipate were confirmed earlier at mid latitudes here we present observations of temperature and velocity fluctuations in the pacific and atlantic oceans between 42 degrees n and 2 degrees s to extend that result to equatorial regions we find a strong latitude dependence of dissipation in accordance with the predictions in our observations dissipation rates and accompanying mixing across density surfaces near the equator are less than 10 of those at mid latitudes for a similar background of internal waves reduced mixing close to the equator will have to be taken into account in numerical simulations of ocean dynamics for example in climate change experiments

near inertial internal waves and sea ice in the beaufort sea the evolution of the near inertial internal wavefield from ice free summertime conditions to ice covered wintertime conditions is examined using data from a yearlong deployment of six moorings on the beaufort continental slope from august 2008 to august 2009 when ice is absent from july to october energy is efficiently transferred from the atmosphere to the ocean generating near inertial internal waves when ice is present from november to june storms also cause near inertial oscillations in the ice and mixed layer but kinetic energy is weaker and oscillations are quickly damped damping is dependent on ice pack strength and morphology decay scales are longer in early winter november january when the new ice pack is weaker and more mobile decreasing in late winter february june when the ice pack is stronger and more rigid efficiency is also reduced as comparisons of atmospheric energy available for internal wave generation to mixed layer kinetic energies indicate that a smaller percentage of atmospheric energy is transferred to nearinertial motions when ice concentrations are 90 however large kinetic energies and shears are observed during an event on 16 december and spectral energy is elevated above garrett munk levels coinciding with the largest energy flux predicted during the deployment a significant amount of near inertial energy is episodically transferred to the internal wave band from the atmosphere even when the ocean is ice covered however damping by ice and less efficient energy transfer still leads to low arctic internal wave energy in the near inertial band increased kinetic energy below 300m when ice is forming suggests some events may generate internal waves that radiate into the arctic ocean interior

the decline in arctic sea ice thickness separating the spatial annual and interannual variability in a quarter century of submarine data 1 naval submarines have collected operational data of sea ice draft 93 of thickness in the arctic ocean since 1958 data from 34 u s cruises are publicly archived they span the years 1975 to 2000 are equally distributed in spring and autumn and cover roughly half the arctic ocean the data set is strong we use 2203 values of mean draft each value averaged over a nominal length of 50 km these values range from 0 to 6 m with a standard deviation of 0 99 m multiple regression is used to separate the interannual change the annual cycle and the spatial field the solution gives a climatology for ice draft as a function of space and time the residuals of the regression have a standard deviation of 0 46 m slightly more than the observational error standard deviation of 0 38 m the overall mean of the solution is 2 97 m annual mean ice draft declined from a peak of 3 42 m in 1980 to a minimum of 2 29 m in 2000 a decrease of 1 13 m 1 25 m in thickness the steepest rate of decrease is 0 08 meters per year m a in 1990 the rate slows to 0 007 m a at the end of the record the annual cycle has a maximum on 30 april and a peak to trough amplitude of 1 06 m 1 12 m in thickness the spatial contour map of the temporal mean draft varies from a minimum draft of 2 2 m near alaska to a maximum just over 4 m at the edge of the data release area 200 miles north of ellesmere island

near inertial wave propagation in the western arctic abstract from october 1997 through october 1998 the surface heat budget of the arctic sheba ice camp drifted across the western arctic ocean from the central canada basin over the northwind ridge and across the chukchi cap during much of this period the velocity and shear fields in the upper ocean were monitored by doppler sonar near inertial internal waves are found to be the dominant contributors to the superinertial motion field typical rms velocities are 1 2 cm s 1 in this work the velocity and shear variances associated with upward and downward propagating wave groups are quantified patterns are detected in these variances that correlate with underlying seafloor depth these are explored with the objective of assessing the role that these extremely low energy near inertial waves play in the larger scale evolution of the canada basin the specific focus is the energy flux delivered to the slopes and shelves of the basin available for driving mixing at the ocean boundaries the energy and

revisiting internal waves and mixing in the arctic ocean 1 to determine whether deep background mixing has increased with the diminishment of the arctic sea ice we compare recent internal wave energy and mixing observations with historical measurements since 2007 the north pole environmental observatory has launched expendable current probes xcps as a part of annual airborne hydrographic surveys in the central arctic ocean mixing in the upper 500 m is estimated from xcp shear variance and conductivity temperature depth ctd derived brunt vaisala frequency internal wave energy levels vary by an order of magnitude between surveys although all surveys are less energetic and show more vertical modes than typical midlatitude garrett munk gm model spectra survey averaged mixing estimates also vary by an order of magnitude among recent surveys comparisons between modern and historical data reanalyzed in identical fashion reveal no trend evident over the 30 year period in spite of drastic diminution of the sea ice turbulent heat fluxes are consistent with recent double diffusive estimates both mixing and internal wave energy in the beaufort sea are lower when compared to both the central and eastern arctic ocean and expanding the analysis to mooring data from the beaufort sea reveals little change in that area compared to historical results from arctic internal wave experiment we hypothesize that internal wave energy remains lowest in the beaufort sea in spite of dramatic declines in sea ice there because increased stratification amplifies the negative effect of boundary layer dissipation on internal wave energy

vertical heat transfer in the arctic ocean the role of double diffusive mixing 1 microstructure profiles collected in the central amundsen basin are analyzed in order to quantify the role of double diffusive mixing for vertical heat transfer from the atlantic layer in the profiles a persistent but laterally incoherent thermohaline staircase structure is identified in the 200 260 m depth range the staircase contains homogeneous layers with average height of 1 3 m and thin high gradient interfaces with average temperature and salinity jumps of about 0 065 c and 0 015 respectively when inferred from a commonly used diffusive convection parameterization the average vertical heat flux within the staircase is 0 6 w m 2 this is one order of magnitude larger than the molecular diffusion alone and of the same order as the overall heat loss from the atlantic layer in the deep basins of the arctic ocean the parameterization is evaluated using observed turbulent heat fluxes and is found to overestimate diffusive convective fluxes with up to an order of magnitude especially for weak thermal forcing small temperature jumps in staircase staircases coexist with thermohaline intrusions in the vertical temperature and salinity profiles lomonosov ridge is identified as a potential region for formation of intrusions it is found that salt fingering is the dominant process during intrusion growth whereas diffusive convection is the dominant process in maintaining the intrusions at steady state in the deep basins

vertical diffusivity of the western arctic ocean halocline a nearly year long series of upper ocean temperature conductivity and temperature microstructure profiles were collected from an ice camp drifting in the beaufort gyre as part of the 1997 1998 surface heat budget of the arctic experiment sheba geographically the record includes portions over the deep canada basin and the steep bathymetry of the chukchi borderlands region hydrographically the record includes cool pacific origin haloclines which contain a variety of subsurface temperature maxima and cold haloclines typical of the eurasian basins we present estimates of the vertical turbulent diffusivity derived from the dissipation rate of thermal variance and calculations of the associated vertical heat fluxes we find that vertical diffusion proceeds at molecular rates in the deep basins and away from topographic features while still relatively small diffusivity is enhanced by 1 order of magnitude near and above the chukchi borderlands the enhanced diffusivity is correlated to an increase in water column strain variance above the borderlands providing a linkage between bathymetry internal wave activity and turbulence the chukchi borderlands play a significant role in heat transport in the western arctic they are a pathway for horizontal heat transport and a hot spot for vertical heat transport vertical fluxes make a substantial contribution to the energy balance of the sea ice cover in this region heat fluxes between the halocline and underlying atlantic water are shown to be small and lacking vertical connection near surface waters

simulating transient ice ocean ekman transport in the regional arctic system model and community earth system model this work evaluates the fidelity of the polar marine ekman layer in the regional arctic system model rasm and community earth system model cesm using sea ice inertial oscillations as a proxy for ice ocean ekman transport a case study is presented that demonstrates that rasm replicates inertial oscillations in close agreement with motion derived using the gps this result is obtained from a year long case study pre dating the recent decline in perennial arctic sea ice using rasm with sub hourly coupling between the atmosphere sea ice and ocean components to place this work in context the rasm coupling method is applied to cesm increasing the frequency of oceanic flux exchange from once per day in the standard cesm configuration to every 30 min for a single year simulation this change causes a considerable increase in the median inertial ice speed across large areas of the southern ocean and parts of the arctic sea ice zone the result suggests that processes associated with the passage of storms over sea ice e g oceanic mixing sea ice deformation and surface energy exchange are underestimated in earth system models that do not resolve inertial frequencies in their marine coupling cycle

ice tethered profiler observations of the double diffusive staircase in the canada basin thermocline vertical heat fluxes through the staircase are in the range 0 05 0 3 w m 2 only about one tenth of the estimated mean surface mixed layer heat flux to the sea ice it is thus concluded that the vertical transport of heat from the atlantic water in the central basin is unlikely to have a significant impact to the canada basin ocean surface heat budget icebreaker conductivity temperature depth data from the beaufort gyre freshwater experiment show that the staircase is absent at the basin periphery turbulent mixing that presumably disrupts the staircase might drive greater flux from the atlantic water at the basin boundaries and possibly dominate the regionally averaged heat flux

observations of internal gravity waves under the arctic pack ice internal gravity waves measured under the arctic pack ice were strikingly different from measurements at lower latitudes the total wave energy integrated over the internal wave frequency band was lower by a factor of 0 03 0 07 and the spectral slope at high frequency was nearly 1 in contrast to the 2 observed at lower latitudes this result has implications for theoretical investigations of the generation evolution and destruction of internal waves and is also important for other processes such as the propagation of sound and the wave induced turbulent diffusion of heat plankton and chemical tracers

global abyssal mixing inferred from lowered adcp shear and ctd strain profiles abstract internal wave wave interaction theories and observations support a parameterization for the turbulent dissipation rate e and eddy diffusivity k that depends on internal wave shear vz2 and strain z2 variances its latest incarnation is applied to about 3500 lowered adcp ctd profiles from the indian pacific north atlantic and southern oceans inferred diffusivities k are functions of latitude and depth ranging from 0 03 10 4 m2 s 1 within 2 of the equator to 0 4 0 5 10 4 m2 s 1 at 50 70 diffusivities k also increase with depth in tropical and subtropical waters diffusivities below 4500 m depth exhibit a peak of 0 7 10 4 m2 s 1 between 20 and 30 latitudes where semidiurnal parametric subharmonic instability is expected to be active turbulence is highly heterogeneous though the bulk of the vertically integrated dissipation e is contributed from the main pycnocline hotspots in e show some correlation with small scale bottom roughness and near bottom flow at sites where st

mixing across the arctic ocean microstructure observations during the beringia 2005 expedition 1 turbulent scale temperature and conductivity were measured during the pan arctic beringia 2005 expedition the rates of dissipation of thermal variance and diapycnal diffusivities are calculated along a section from alaska to the north pole across deep flat basins canada and makarov basins and steep ridges alpha mendeleev and lomonosov ridges the mixing rates are observed to be small relative to lower latitudes but also remarkably non uniform relatively elevated turbulence is found over deep topography confirming the dominant role of bottom generated internal waves measured patterns of mixing in the arctic are also associated with other mechanisms such as double diffusive structures and deep overflows a better knowledge of the distribution of mixing is essential to understand the dynamics of the changing arctic environment

retreat of the cold halocline layer in the arctic ocean we present a comparison of arctic ocean hydrographic data sets from the 1990s with a focus on changes in the upper few hundred meters of the eurasian basin the most recent observations discussed here were collected during the spring 1995 scientific ice expedition scicex 95 the second in a series of scientific cruises to the arctic ocean aboard u s navy nuclear submarines although the 1990s have seen an abundance of synoptic cruises to the arctic this was the only one to take place in winter spring conditions other data considered here were collected during the first scicex cruise in summer 1993 scicex 93 and during an icebreaker cruise to the eurasian basin in summer 1991 oden 91 a new russian american winter climatology is also used as a reference these comparisons reveal that the eurasian basin cold halocline layer has retreated during the 1990s to cover significantly less area than in previous years specifically we find a retreat from the amundsen basin back into the makarov basin the latter is the only region with a true cold halocline layer during scicex 95 changes are also seen in other halocline types and in the atlantic water layer heat content and depth since the cold halocline layer insulates the surface layer and thus the overlying sea ice from the heat contained in the atlantic water layer this should have profound effects on the surface energy and mass balance of sea ice in this region using a simple mixing model we calculate maximum ice ocean heat fluxes of 1 3 w m 2 in the eurasian basin where during scicex 95 the surface layer lay in direct contact with the underlying atlantic water layer the overall cause of water mass changes in the 1990s might have been a shift in the atmospheric wind forcing and resulting sea ice motion during the late 1980s which we speculate influenced the location where fresh shelf waters flow into the deeper basins of the arctic ocean finally we discuss two different mechanisms that have been proposed for cold halocline water formation and we propose a compromise that best fits these data

upper ocean velocities in the beaufort gyre a 23 month time series of upper ocean velocities in the beaufort gyre was obtained from an autonomous drifting buoy equipped with an acoustic doppler current profiler the buoy was deployed in the beaufort sea and drifted over the canada basin chukchi shelf and chukchi plateau time evolving spectral analysis was used to examine velocity variability in three frequency bands an eddy band 2 5 day periods a diurnal band and a semidiurnal band the eddy band and the semidiurnal band dominated the horizontal kinetic energy although eddy energy was clearly confined to the beaufort sea and canada basin eddies were found further to the south and west than in previous observations the semidiurnal band was dominated by near inertial motions with amplitude that varied seasonally largest in late summer and smallest in late winter diurnal tides were weak 1 cm s 1 except over a shallow portion of the chukchi shelf

near inertial mixing in the central arctic ocean observations were made in april 2007 of horizontal currents hydrography and shear microstructure in the upper 500m from a drifting ice camp in the central arctic ocean an approximately 4 day long time series collected about 10 days after a storm event shows enhanced near inertial oscillations in the first half of the measurement period with comparable upward and downward propagating energy rough estimates of wind work and near inertial flux imply that the waves were likely generated by the previous storm the nearinertial frequency band is associated with dominant clockwise rotation in time of the horizontal currents and enhanced dissipation rates of turbulent kinetic energy the vertical profile of dissipation rate shows elevated values in the pycnocline between the relatively turbulent underice boundary layer and the deeper quiescent water column dissipation averaged in the pycnocline is near inertially modulated and its magnitude decays approximately at a rate implied by the reduction of energy over time observations suggest that near inertial energy and internal wave induced mixing play a significant role in vertical mixing in the arctic ocean

observational validation of the diffusive convection flux laws in the amundsen basin arctic ocean the low levels of mechanically driven mixing in many regions of the arctic ocean make double diffusive convection virtually the only mechanism for moving heat up from the core of atlantic water towards the surface in an attempt to quantify double diffusive heat fluxes in the arctic ocean a temperature microstructure experiment was performed as a part of the north pole environmental observatory npeo 2013 field season from the drifting ice station barneo located in the amundsen basin near the lomonosov ridge 89 5 n 75 w a diffusive convective thermohaline staircase was present between 150 and 250 m in nearly all of the profiles typical vertical heat fluxes across the high gradient interfaces were consistently small o 10 1 w m 2 our experiment was designed to resolve the staircase and differed from earlier arctic studies that utilized inadequate instrumentation or sampling our measured fluxes from temperature microstructure agree well with the laboratory derived flux laws compared to previous studies which could find agreement only to within a factor of two to four correlations between measured and parameterized heat fluxes are slightly higher when using the more recent flanagan et al 2013 laboratory derivation than the more commonly used derivation presented in kelley 1990 nusselt versus rayleigh number scaling reveals the convective exponent to be closer to 0 29 as predicted by recent numerical simulations of single component convection rather than the canonical 1 3 assumed for double diffusion however the exponent appears to be sensitive to how convective layer height is defined

hotspots of deep ocean mixing on the oregon continental slope 1 two deep ocean hotspots of turbulent mixing were found over the oregon continental slope thorpe scale analyses indicate time averaged turbulent energy dissipation rates of e 10 7 w kg and eddy diffusivities of k 10 2 m2 s at both hotspots however the structure of turbulence and its generation mechanism at each site appear to be different at the 2200 m isobath sustained 100 m high turbulent overturns occur in stratified fluid several hundred meters above the bottom turbulence shows a clear 12 4 h periodicity proposed to be driven by flow over a nearby 100 m tall ridge at the 1300 m isobath tidally modulated turbulence of similar intensity is confined within a stratified bottom boundary layer along slope topographic roughness at scales not resolved in global bathymetric data sets appears to be responsible for the bulk of the turbulence observed such topography is common to most continental slopes providing a mechanism for turbulence generation in regions where barotropic tidal currents are nominally along isobath

internal waves and mixing in the marginal ice zone near the yermak plateau observations were made of oceanic currents hydrography and microstructure in the southern yermak plateau in summer 2007 the location is in the marginal ice zone at the arctic front northwest of svalbard where the west spitsbergen current wsc carries the warm atlantic water into the arctic ocean time series of approximately 1 day duration from five stations upper 520 m and of an 8 day duration from a mooring are analyzed to describe the characteristics of internal waves and turbulent mixing the spectral composition of the internal wave field over the southern yermak plateau is 0 1 0 3 times the midlatitude levels and compares with the most energetic levels in the central arctic dissipation rate and eddy diffusivity below the pycnocline increase from the noise level on the cold side of the front by one order of magnitude on the warm side where 100 m thick layers with average diffusivities of 5 3 10 25 m 2 s 21 lead to heat loss from the atlantic water of 2 4 w m 22 dissipation in the upper 150 m is well above the noise level at all stations but strong stratification at the cold side of the front prohibits mixing across the pycnocline close to the shelf at the core of the svalbard branch of the wsc diffusivity increases by another factor of 3 6 here nearbottom mixing removes 15 w m 22 of heat from the atlantic layer internal wave activity and mixing show variability related to topography and hydrography thus the path of the wsc will affect the cooling and freshening of the atlantic inflow when generalized to the arctic ocean diapycnal mixing away from abyssal plains can be significant for the heat budget around the yermak plateau it is of sufficient magnitude to influence heat anomaly pulses entering the arctic ocean however diapycnal mixing alone is unlikely to be significant for regional cooling of the wsc

thermohaline staircases in the amundsen basin possible disruption by shear and mixing as part of the 2013 and 2014 north pole environmental observatories npeo in the amundsen basin of the arctic ocean two similar temperature microstructure experiments were performed with different results in 2013 vertical fluxes were through a thermohaline staircase and in 2014 the thermohaline staircase was largely absent here we investigate the reasons for this difference the 2013 data set was characterized by an extensive thermohaline staircase indicative of the diffusive convective type of double diffusion dc from 120 250 m depths the staircase was absent above 200 m in 2014 even though analysis of density ratio r still shows high susceptibility to ddc in the depth range of interest survey averaged r 3 8 in 2013 and r 3 6 in 2014 indicating that the temperature salinity structure in the pycnocline was not the cause of the lack of a staircase in 2014 we propose that exceptionally weak turbulent mixing even for the typically quiescent arctic ocean allowed formation of the staircase in 2013 average thermal diffusivity kt between 50 120 m is elevated in 2014 2 x 10 5 m2s 1 compared to 2013 1 x 10 6 m2s 1 however vertical atlantic water aw dc heat fluxes in 2013 are remarkably consistent with turbulent heat fluxes in 2014 similar data sets collected in 2007 and 2008 both resemble 2014 showing consistently higher mixing values compared to 2013 the suppression of turbulence during npeo 2013 resulted from increased near surface stratification possibly caused by a different large scale circulation pattern that year

diffusive vertical heat flux in the canada basin of the arctic ocean inferred from moored instruments 1 observational studies have shown that an unprecedented warm anomaly has recently affected the temperature of the atlantic water aw layer lying at intermediate depth in the arctic ocean using observations from four profiling moorings deployed in the interior of the canada basin between 2003 and 2011 the upward diffusive vertical heat flux from this layer is quantified vertical diffusivity is first estimated from a fine scale parameterization method based on ctd and velocity profiles resulting diffusive vertical heat fluxes from the aw are in the range 0 1 0 2 w m 2 on average although large over the period considered the variations of the aw temperature maximum yields small variations for the temperature gradient and thus the vertical diffusive heat flux in most areas variations in upward diffusive vertical heat flux from the aw have only a limited effect on temperature variations of the overlying layer however the presence of eddies might be an effective mechanism to enhance vertical heat transfer although the small number of eddies sampled by the moorings suggest that this mechanism remains limited and intermittent in space and time finally our results suggest that computing diffusive vertical heat flux with a constant vertical diffusivity of 2 10 6 m2 s 1 provides a reasonable estimate of the upward diffusive heat transfer from the aw layer although this approximation breaks down in the presence of eddies

on the interplay between the circulation in the surface and the intermediate layers of the arctic ocean abstractthe circulation of the arctic ocean has traditionally been studied as a two layer system with a wind driven anticyclonic gyre in the surface layer and a cyclonic boundary current in the atlantic water aw layer primarily forced remotely through inflow and outflow to the basin here an idealized numerical model is used to investigate the interplay between the dynamics of the two layers and to explore the response of the circulation in each of the layers to a change in the forcing in either layer in the model the intensity of the circulation in the surface and aw layers is primarily set by the ocean surface stress curl intensity and the inflow to the basin respectively additionally the surface layer circulation can strongly modulate the intensity of the intermediate layer by constraining the lateral extent of the aw current on the slope in contrast a change in the aw current strength has little effect on the surface layer circulation the intensity of the circulation in the surface layer

beaufort gyre freshwater reservoir state and variability from observations 1 we investigate basin scale mechanisms regulating anomalies in freshwater content fwc in the beaufort gyre bg of the arctic ocean using historical observations and data collected in 2003 2007 specifically the mean annual cycle and interannual and decadal fwc variability are explored the major cause of the large fwc in the bg is the process of ekman pumping ep due to the arctic high anticyclonic circulation centered in the bg the mean seasonal cycle of liquid fwc is a result of interplay between the mechanical ep and thermal ice transformations factors and has two peaks one peak occurs around june july when the sea ice thickness reaches its minimum maximum ice melt the second maximum is observed in november january when wind curl is strongest maximum ep and the salt input from the growing ice has not yet reached its maximum interannual changes in fwc during 2003 2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a 1 in the center of ep influenced region decadal fwc variability in the period 1950 2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change the center of maximum fwc shifted to the southeast and appeared to contract in area relative to the pre 1990s climatology in spite of the areal reduction the spatially integrated fwc increased by over 1000 km 3 relative to climatology