barotropic tides in the global oceans from a nonlinear tidal model assimilating altimetric tides 1 model description and results in this first part of a two part paper we present results from a high resolution data assimilative fully nonlinear barotropic tidal model of the global oceans that excludes the arctic the model assimilates in waters deeper than 1000 m altimetric tides derived from the analysis of 2 years of topex altimetric data it also assimilates tide gage data from coastal tide gages the model domain includes that covered by the altimeter and extends to the antarctic in the first part we present tidal results for the primary semidiurnal m2 s2 n2 and k2 and diurnal k1 o1 p1 and q1 constituents the second part deals with applications kantha et al this issue the model results are compared with observational data from pelagic gages these comparisons show that overall in the open ocean in deep waters away from the margins of the primary basins the model performance is comparable to other tidal models derived using topex data except for m2 and s2 however one advantage of this model compared with those based solely on the analysis of altimetric data is that the altimetry derived tides are subjected to dynamical constraints by the model this results in reduction of subtidal variability often folded into tidal signals by topex data analysis it is also shown that in shallow waters along the margins especially in east asian marginal seas the model differs substantially from these other models in addition to sea surface heights we also present dynamically consistent barotropic currents in the form of tidal ellipses for m2 and k1 constituents since the goal of this research is a global tidal model uniformly valid in both deep and shallow waters we finally present tidal elevations and currents on two well known shallow water areas the northwest european shelf and the northeast american shelf and a semienclosed western pacific marginal sea the bering sea the model results are compared with independent observations and where possible with results from other numerical models the results highlight the importance of bottom topography on the northwest european shelf where accurate bottom topography was included in the model the results are much better than on the northeast american shelf where the digital bathymetric data base 5 dbdb5 topographic database has significant errors results from the bering sea where the topography is more accurate than the dbdb5 compare well with known tides in the region

topographic amplitude dependence of internal wave generation by tidal forcing over idealized three dimensional topography 1 this numerical study using the princeton ocean model investigates the conversion of energy from an eastward propagating surface tide to the internal wave field as an oscillating tidal current flows over and around idealized three dimensional gaussian seamounts in particular the relationship between the energy flux in the internal wave field and the height of the topography is explored using a range of horizontal aspect ratios in agreement with theory the energy flux is found to increase as the square of the topographic amplitude ho for subcritical topography for supercritical topographies the functional relationship is more complex aspect ratio dependent it increases more rapidly than ho2 for near critical topography for larger circular seamounts the energy flux increases much more slowly with the rate of increase dropping with amplitude as the seamounts are elongated in the cross tidal wave north south direction the energy flux increases more rapidly with height and for a two dimensional ridge increases as approximately ho2 2 the directional dependence of the energy flux also depends on the aspect ratio and amplitude of the seamount for circular seamounts energy flux has its maximum in directions between 20 and 45 counterclockwise from the east west axis northern hemisphere for elongated seamounts the energy flux is directed in the east west direction

abyssal circulation driven by near boundary mixing water mass transformations and interior stratification the emerging view of the abyssal circulation is that it is associated with bottom enhanced mixing which results in downwelling in the stratified ocean interior and upwelling in a bottom boundary layer along the insulating and sloping seafloor in the limit of slowly varying vertical stratification and topography however boundary layer theory predicts that these upslope and downslope flows largely compensate such that net water mass transformations along the slope are vanishingly small using a planetary geostrophic circulation model that resolves both the boundary layer dynamics and the large scale overturning in an idealized basin with bottom enhanced mixing along a midocean ridge we show that vertical variations in stratification become sufficiently large at equilibrium to reduce the degree of compensation along the midocean ridge flanks the resulting large net transformations are similar to estimates for the abyssal ocean and span the vertical extent of the ridge these results suggest that boundary flows generated by mixing play a crucial role in setting the global ocean stratification and overturning circulation requiring a revision of abyssal ocean theories

deep sea fluid and sediment dynamics influence of hill to seamount scale seafloor topography abstract deep sea sediments play a central role in a wide range of subject areas a number of important controls on the formation of sedimentary deposits have been studied however to date the impact of submarine landscape geometry as a possible control has received comparatively little attention this seems to be particularly true for intermediate scale topographic features such as abyssal hills knolls and seamounts that can be found in many regions of the global seafloor recent estimates suggest that in the deep open oceans away from continental margins there might be as many as 25 106 abyssal hills knolls and seamounts despite this large number very little is known about how they influence environmental complexity and patchiness biogeochemical fluxes and the formation of sedimentary records this paper reviews the currently known types of fluid flow interactions with abyssal hills knolls and seamounts that could potentially influence the way sediments are formed the main types of relevant flow components are quasi steady to eddying background flow internal lee and near inertial waves barotropic and baroclinic tides and seamount trapped waves previous studies looking into systematic links between fluid dynamics and sediments at hills knolls and seamounts are reviewed finally a case study is presented which aims to combine our current knowledge and investigate whether a given combination of recent fluid flow components leaves a detectable imprint in the recent sediments on and around a short seamount the main conclusions and implications are as follows 1 topographically generated flow field geometries that are composed of a number of different prevailing fluid flow components can be reflected and detected in properties of the underlying sediments 2 tidal and other higher frequency lee wave near inertial components of deep ocean currents can be essential for locally driving total current velocities across threshold values for non deposition erosion resuspension of freshly deposited deep sea sediments moreover there is evidence suggesting that not only maximum current speeds but also intensities of higher frequency tidal and or near inertial current direction variability might control sediment dynamics and sediment formation this relativises the view that current speed is the main or even only controlling factor for sediment dynamics and sediment formation 3 when it comes to the reconstruction of paleo flows these findings imply that certain sedimentary records may well reveal more about variability in the higher frequency flow components than about variability in the basin scale net flow component that often is the focus of paleoceanographic studies 4 single core paleo records from hill seamount or similarly controlled sediment deposits may be biased due to the asymmetry of flow fields around these topographic features to arrive at unbiased paleo records for non fluid dynamic parameters the influence of the flow field geometry would have to be removed from the record first 5 it seems the mechanistic understanding of hill and seamount related flow topography interactions and their links to sediment dynamics is approaching a level that may a facilitate improved interpretation of topographically controlled sedimentary paleo records b help fill in the knowledge gap that exists for functional deep sea biodiversity at intermediate space scales and c improve predictive capabilities for exploration of economically relevant iron manganese fe mn crusts on seamounts

post equinox dynamics and polar cloud structure on uranus abstract post equinox imaging of uranus by hst keck and gemini telescopes has enabled new measurements of winds over previously sampled latitudes as well as measurements at high northern latitudes that have recently come into better view these new observations also used techniques to greatly improve signal to noise ratios making possible the detection and tracking of more subtle cloud features the 250 m s prograde jet peaking near 60 n was confirmed and more accurately characterized several long lived cloud features have also been tracked the winds pole ward of 60 n are consistent with solid body rotation at a westward prograde rate of 4 3 h with respect to uranus interior when combined with 2007 and other recent measurements it is clear that a small but well resolved asymmetry exists in the zonal profile at middle latitudes peaking at 35 where southern winds are 20 m s more westward than corresponding northern winds high s n keck ii imaging of the north polar region of uranus reveals a transition from streaky bands below 60 n to a region from 60 to nearly the north pole where widely distributed small bright spots resembling cumulus cloud fields with several isolated dark spots are the dominant style of cloud features this presents a stark contrast to 2003 detailed views of the south polar region of uranus when no discrete cloud features could be detected in comparable keck ii near ir images the pressure levels of discrete clouds estimated from spatial modulations in h and hcont images indicate that the polar cloud features are generally in the 1 3 to 2 3 bar range as are equatorial and several mid latitude features several of the brighter mid latitude features are found above the 1 2 bar level of methane condensation

mid ocean ridges fine scale tectonic volcanic and hydrothermal processes within the plate boundary zone a first order model of spreading centers as idealized linear boundaries of crustal and lithospheric generation provides only a gross understanding of global scale plate kinematics as we attempt to understand the complexity of crustal and lithospheric structure of two thirds of the earth s surface it is becoming increasingly necessary to study the tectonic volcanic and hydro thermal processes within the spreading center plate boundary zone all ocean ic crust bears the imprint of these processes this review focuses on a few selected topics concernining the fine scale tectonics and geophysics of the active axial zone of mid ocean ridges with reference to associated volcanic and hydrothermal processes it draws heavily on recent studies that use deeply towed instrument packages multi beam bathymetric mapping ocean bottom instruments and alvin e g the famous amar rise and galapagos expeditions we begin with a review of the large scale structure of spreading centers we then take a close look at the axial neovolcanic zone and progress away from the axis through the active tectonic zones next we consider the characteristics of the axial magma chamber and associated hydrothermal actvity as well as the generation of magnetic anomaly stripes and their implications for crustal generation one of our findings is that the initial two dimensional model of volcanic and tectonic zones must be expanded upon to allow for variations

the 8 2 ka event abrupt transition of the subpolar gyre toward a modern north atlantic circulation 1 climate model simulations of the 8 2 ka event show an abrupt strengthening of the atlantic subpolar gyre that allows us to connect two major but apparently contradictory climate events of the early holocene the freshwater outburst from proglacial lakes and the onset of labrador sea water formation the 8 2 ka event is the largest climatic signal of our present interglacial with a widespread cooling in the north atlantic region about 8200 years before present it coincides with a meltwater outburst from north american proglacial lakes that is believed to have weakened the atlantic meridional overturning circulation and northward heat transport followed by a recovery of the deep ocean circulation and rising temperatures after a few centuries marine proxy data however date the onset of deep water formation in labrador sea to the same time the subsequent strengthening of the slope current system created a regional signal recorded as an abrupt and persistent surface temperature decrease although similarities in timing are compelling a mechanism to reconcile these apparently contradictory events was missing our simulations show that an abrupt and persistent strengthening of the atlantic subpolar gyre provides a plausible explanation the intense freshwater pulse triggered a transition of the gyre circulation into a different mode of operation stabilized by internal feedbacks and persistent after the cessation of the perturbation as a direct consequence deep water formation around its center intensifies this corresponds to the modern flow regime and stabilizes the meridional overturning circulation possibly contributing to the holocene s climatic stability

uranus at equinox cloud morphology and dynamics abstract as the 7 december 2007 equinox of uranus approached collaboration between ring and atmosphere observers in the summer and fall of 2007 produced a substantial collection of ground based observations using the 10 m keck telescope with adaptive optics and space based observations with the hubble space telescope both near infrared and visible wavelength imaging and spatially resolved near infrared spectroscopic observations were obtained we used observations spanning the period from 7 june 2007 through 9 september 2007 to identify and track cloud features determine atmospheric motions characterize cloud morphology and dynamics and define changes in atmospheric band structure atmospheric motions were obtained over a wider range of latitudes than previously was possible extending to 73 n and for 28 cloud features we obtained extremely high wind speed accuracy through extended tracking times we confirmed the existence of the suspected northern hemisphere prograde jet locating its peak near 58 n the new results confirm a small n s asymmetry in the zonal wind profile and the lack of any change in the southern hemisphere between 1986 near solstice and 2007 near equinox suggests that the asymmetry may be permanent rather than seasonally reversing in the 2007 images we found two prominent groups of discrete cloud features with very long lifetimes the one near 30 s has departed from its previous oscillatory motion and started a significant northward drift accompanied by substantial morphological changes the complex of features near 30 n remained at a nearly fixed latitude while exhibiting some characteristics of a dark spot accompanied by bright companion features smaller and less stable features were used to track cloud motions at other latitudes some of which lasted over many planet rotations though many could not be tracked beyond a single transit a bright band has developed near 45 n while the bright band near 45 s has begun to decline both events in agreement with the idea that the asymmetric band structure of uranus is a delayed response to solar forcing but with a surprisingly short delay of only a few years

on the accuracy of digital bathymetric data the global 5 arcmin gridded topography data etopo 5 are based on contour maps rather than original soundings and have large errors the artificial statistical distribution generated by digitizing contours makes these data unsuitable for use in regression models for depth age variations their amplitude spectrum is bounded by a frequency 4 power law so that they should not be used when the gravity topography transfer function is important such as in studies of flexural isostasy and mantle convection i assess the accuracy of 14 491 069 digital ship soundings in 2253 cruise surveys collected between 1955 and 1992 in the lamont doherty earth observatory on line data base by analyzing 329 058 crossover errors coes at intersecting ship tracks five percent of cruises with internal coes yield root mean square coe amplitudes exceeding 500 m all of these have errors in digitizing two way travel time from analog precision depth recorder traces twenty eight cruises were found which had errors caused by misinterpretation of the nominal sound velocity used when travel times were reported as nominal depths two nominal sound velocities in common use differ by 2 5 an amount which is often undetectable producing uncertainties in depth of this magnitude ship data have been acquired at different rates over time with the peak of activity in the early 1970s although present technologies can yield very accurate data these are acquired at a rate which is small with respect to the total available data the cumulative median global coe has remained constant at 26 m since the late 1970s most recent data acquisition has been in the northern hemisphere oceans and the oldest and least accurate data are in the southern oceans where median coes are 100 250 m the majority of the data in the south pacific were acquired before the advent of satellite navigation

high s n keck and gemini ao imaging of uranus during 2012 2014 new cloud patterns increasing activity and improved wind measurements abstract we imaged uranus in the near infrared from 2012 into 2014 using the keck nirc2 camera and gemini niri camera both with adaptive optics we obtained exceptional signal to noise ratios by averaging 8 16 individual exposures in a planet fixed coordinate system these noise reduced images revealed many low contrast discrete features and large scale cloud patterns not seen before including scalloped waveforms just south of the equator and an associated transverse ribbon wave near 6 s in all three years numerous small 600 700 km wide and mainly bright discrete features were seen within the north polar region north of about 55 n two small dark spots with bright companions were seen at middle latitudes over 850 wind measurements were made the vast majority of which were in the northern hemisphere winds at high latitudes were measured with great precision revealing an extended region of solid body rotation between 62 n and at least 83 n at a rate of 4 08 0 015 h westward relative to the planet s interior radio rotation of 20 88 h westward near equatorial speeds measured with high accuracy give different results for waves and small discrete features with eastward drift rates of 0 4 h and 0 1 h respectively the region of polar solid body rotation is a close match to the region of small scale polar cloud features suggesting a dynamical relationship the winds from prior years and those from 2012 2014 are consistent with a mainly symmetric wind profile up to middle latitudes with a small asymmetric component of 0 09 h peaking near 30 and about 60 greater amplitude if only prior years are included suggesting a declining mid latitude asymmetry while winds at high southern latitudes 50 90 s are unconstrained by groundbased observations a recent reanalysis of 1986 voyager 2 observations by karkoschka karkoschka 2015 icarus 250 294 307 has revealed an extremely large north south asymmetry in this region which might be seasonal greatly increased activity was seen in 2014 including the brightest ever feature seen in k images de pater et al 2015 icarus 252 121 128 as well as other significant features some of which had long lives over the 2012 2014 period we identified six persistent discrete features three were tracked for more than 2 years two more for more than 1 year and one for at least 5 months and continuing several drifted in latitude towards the equator and others appeared to exhibit latitudinal oscillations with long periods we found two pairs of long lived features that survived multiple passages within their own diameters of each other zonally averaged cloud patterns were found to persist over 2012 2014 when averaged over longitude there is a brightness variation with latitude from 55 n to the pole that is similar to effective methane mixing ratio variations with latitude derived from 2012 stis observations sromovsky et al 2014 icarus 238 137 155

parameterizing tidal dissipation over rough topography the traditional model of tidal dissipation is based on a frictional bottom boundary layer in which the work done by bottom drag is proportional to a drag coefficient and the velocity cubed however away from shallow coastal regions the tidal velocities are small and the work done by the bottom boundary layer can account for only weak levels of dissipation in the deep ocean the energy flux carried by internal waves generated over rough topography dominates the energy transfer away from barotropic flow a parameterization for the internal wave drag over rough topography is included as a dissipative mechanism in a model for the barotropic tides model results suggest that the inclusion of this dissipation mechanism improves hydro dynamical models of the ocean tide it also substantially increases the amount of modeled tidal dissipation in the deep ocean bringing dissipation levels there into agreement with recent estimates from topex poseidon altimetry data

neptune s global circulation deduced from multi wavelength observations abstract we observed neptune between june and october 2003 at near and mid infrared wavelengths with the 10 m w m keck ii and i telescopes respectively and at radio wavelengths with the very large array images were obtained at near infrared wavelengths with nirc2 coupled to the adaptive optics system in both broad and narrow band filters between 1 2 and 2 2 m in the mid infrared we imaged neptune at wavelengths between 8 and 22 m and obtained slit resolved spectra at 8 13 m and 18 22 m at radio wavelengths we mapped the planet in discrete filters between 0 7 and 6 cm we analyzed each dataset separately with a radiative transfer program that is optimized for that particular wavelength regime at southern midlatitudes the atmosphere appears to be cooler at mid infrared wavelengths than anywhere else on the planet we interpret this to be caused by adiabatic cooling due to air rising at midlatitudes at all longitudes from the upper troposphere up to 0 1 mbar levels at near infrared wavelengths we find two distinct cloud layers at these latitudes a relatively deep layer of clouds presumably methane in the troposphere at pressure levels p 300 600 mbar which we suggest to be caused by the large scale upwelling and its accompanying adiabatic cooling and condensation of methane and a higher spatially intermittent layer of clouds in the stratosphere at 20 30 mbar the latitudes of these high clouds encompass an anticyclonic band of zonal flow which suggests that they may be due to strong but localized vertical upwellings associated with local anticyclones rather than plumes in convective i e cyclonic storms clouds at northern midlatitudes are located at the highest altitudes in the atmosphere near 10 mbar neptune s south pole is considerably enhanced in brightness at both mid infrared and radio wavelengths i e from 0 1 mbar levels in the stratosphere down to tens of bars in the troposphere we interpret this to be due to subsiding motions from the stratosphere all the way down to the deep troposphere the enhanced brightness observed at mid infrared wavelengths is interpreted to be due to adiabatic heating by compression in the stratosphere and the enhanced brightness temperature at radio wavelengths reveals that the subsiding air over the pole is very dry the relative humidity of h 2 s over the pole is only 5 at altitudes above the nh 4 sh cloud at 40 bar the low humidity region extends from the south pole down to latitudes of 66 s this is near the same latitudes as the south polar prograde jet signifying the boundary of the polar vortex we suggest that the south polar features spfs at latitudes of 60 70 are convective storms produced by baroclinic instabilities expected to be produced at latitudes near the south polar prograde jet taken together our data suggest a global circulation pattern where air is rising above southern and northern midlatitudes from the troposphere up well into the stratosphere and subsidence of dry air over the pole and equator from the stratosphere down into the troposphere we suggest that this pattern extends all the way from 0 1 mbar down to pressures of 40 bar

convective storms and atmospheric vertical structure in uranus and neptune the ice giants uranus and neptune have hydrogen based atmospheres with several constituents that condense in their cold upper atmospheres a small number of bright cloud systems observed in both planets are good candidates for moist convective storms but their observed properties size temporal scales and cycles of activity differ from moist convective storms in the gas giants these clouds and storms are possibly due to methane condensation and observations also suggest deeper clouds of hydrogen sulfide h2s at depths of a few bars even deeper thermochemical models predict clouds of ammonia hydrosulfide nh4sh and water at pressures of tens to hundreds of bars forming extended deep weather layers because of hydrogen s low molecular weight and the high abundance of volatiles their condensation imposes a strongly stabilizing vertical gradient of molecular weight larger than the equivalent one in jupiter and saturn the resulting inhibition of vertical motions should lead to a moist convective regime that differs significantly from the one occurring on nitrogen based atmospheres like those of earth or titan as a consequence the thermal structure of the deep atmospheres of uranus and neptune is not well understood similar processes might occur at the deep water cloud of jupiter in saturn but the ice giants offer the possibility to study these physical aspects in the upper methane cloud layer a combination of orbital and in situ data will be required to understand convection and its role in atmospheric dynamics in the ice giants and by extension in hydrogen atmospheres including jupiter saturn and giant exoplanets this article is part of a discussion meeting issue future exploration of ice giant systems

internal tides and vertical mixing over the kerguelen plateau within the context of the natural iron fertilization study keops time series measurements of ctd and ladcp profiles at a site 50 6 s 72 e 528 m coinciding with an annual phytoplankton bloom over the kerguelen plateau were made during the january february 2005 keops cruise an important activity of highly nonlinear semidiurnal internal tides having peak to peak isopycnal displacements of up to 80 m is identified these internal tides appear to be a principal agent for promoting elevated vertical mixing indispensable for upward transfer of iron within the seasonal thermocline we estimate local vertical eddy diffusivities of the order of 4 10 4 m2 s 1 using a thorpe scale analysis although this estimate is higher by an order of magnitude than the canonical value o 0 1 10 4 m2 s 1 in the open ocean away from boundaries it is consistent with nonlinear internal wave wave interaction theories as verified by independent diffusivity estimates using the vertical wavenumber spectral methods for shear and strain it is also suggested that the general ocean circulation may play an important role in preconditioning the bloom in that the relatively sluggish circulation over the shallow plateau compared to the much more dynamic neighbouring deep ocean may foster the bloom s observed annual recurrence over the plateau

on the influence of wind stress curl on low frequency shelf water flow abstract an approximate solution for wind driven near barotropic flow over the continental shelf is obtained the solution shows that a wind stress with amplitude that increases offshore and then is relatively constant as observed during the coastal ocean dynamics experiments code results in two types of shear the horizontal shear is associated with the offshore increase of the wind stress which strengthens the flow the vertical shear is associated with the alongshore wind stress amplitude and its first two offshore derivatives for a wind stress structure similar to the one observed during code the dominant vertical shear is associated with 2 y x2 where y is the alongshore wind stress and x is the distance seaward from the coast physically 2 y x2 nonzero means that the surface ekman pumping will vary with x tilt isopycnals and produce a vertical shear in the alongshore velocity in accordance with the thermal wind relation the near barotropic solution for the alongshore velocity field

seafloor tectonic fabric from satellite altimetry abstract ocean floor structures with horizontal scales of 10 to a few hundred kilometers and vertical scales of 100 m or more generate sea surface gravity anomalies observable with satellite altimetry prior to 1990 altimeter data resolved only tectonic lineaments some seamounts and some aspects of mid ocean ridge structure new altimeter data available since mid 1995 resolve 10 km scale structures over nearly all the world s oceans these data are the basis of new global bathymetric maps and have been interpreted as exhibiting complexities in the sea floor spreading process including ridge jumps propagating rifts and variations in magma supply this chapter reviews the satellite altimetry technique and its resolution of tectonic structures gives examples of intriguing tectonic phenomena and shows that structures as small as abyssal hills are partially resolved a new result obtained here is that the amplitude of the fine scale 10 80 km roughness of old ocean floor is spreading rate dependent i

a correspondence of altimetric gravity texture to abyssal hill morphology along the flanks of the southeast indian ridge 1 we examine the relationship between altimetric gravity and abyssal hill textures along the flanks of southeast indian ridge where previous studies observed a progressive west to east increase in abyssal hill roughness and scales such a relationship is often considered unlikely because abyssal hills are typically smaller than upward continuation filter scales however our results which exclude ridges fracture zones and large pseudofaults show that altimetric gravity roughness and characteristic scales in this region also increase from west to east and at the largest scales gravity texture exhibits ridge parallel lineaments synthetic profiles also demonstrate how the texture parameters of a filtered field are related to those of the unfiltered field particularly where the characteristic scale of the latter is smaller than the filter length

global energy conversion rate from geostrophic flows into internal lee waves in the deep ocean a global estimate of the energy conversion rate from geostrophic flows into internal lee waves in the ocean is presented the estimate is based on a linear theory applied to bottom topography at o 1 10 km scales obtained from single beam echo soundings to bottom stratification estimated from climatology and to bottom velocity obtained from a global ocean model the total energy flux into internal lee waves is estimated to be 0 2 tw which is 20 of the global wind power input into the ocean the geographical distribution of the energy flux is largest in the southern ocean which accounts for half of the total energy flux the results suggest that the generation of internal lee waves at rough topography is a significant energy sink for the geostrophic flows as well as an important energy source for internal waves and the associated turbulent mixing in the deep ocean

revised vertical cloud structure of uranus from ukirt uist observations and changes seen during uranus northern spring equinox from 2006 to 2008 application of new methane absorption data and comparison with neptune abstract long slit spectroscopy observations of uranus by the united kingdom infrared telescope uist instrument in 2006 2007 and 2008 have been used to monitor the change in uranus vertical and latitudinal cloud structure through the planet s northern spring equinox in december 2007 these spectra were analysed and presented by irwin et al irwin p g j teanby n a davis g r 2009 icarus 203 287 302 but since publication a new set of methane absorption data has become available karkoschka e tomasko m 2010 methane absorption coefficients for the jovian planets from laboratory huygens and hst data icarus 205 674 694 which appears to be more reliable at the cold temperatures and high pressures of uranus deep atmosphere we have fitted k coefficients to these new methane absorption data and we find that although the latitudinal variation and inter annual changes reported by irwin et al 2009 stand the new k data place the main cloud deck at lower pressures 2 3 bars than derived previously in the h band of 3 4 bars and 3 bars compared with 6 bars in the j band indeed we find that using the new k data it is possible to reproduce satisfactorily the entire observed centre of disc uranus spectrum from 1 to 1 75 m with a single cloud at 2 3 bars provided that we make the particles more back scattering at wavelengths less than 1 2 m by for example increasing the assumed single scattering albedo from 0 75 assumed in the j and h bands to near 1 0 in addition we find that using a deep methane mole fraction of 4 in combination with the associated warm f temperature profile of lindal et al lindal g f lyons j r sweetnam d n eshleman v r hinson d p 1987 j geophys res 92 14987 15001 the retrieved cloud deck using the new karkoschka and tomasko 2010 methane absorption data moves to between 1 and 2 bars the same methane absorption data and retrieval algorithm were applied to observations of neptune made during the same programme and we find that we can again fit the entire 1 1 75 m centre of disc spectrum with a single cloud model providing that we make the stratospheric haze particles of much greater opacity than for uranus conservatively scattering i e 1 and we also make the deeper cloud particles again at around the 2 bar level more reflective for wavelengths less than 1 2 m hence apart from the increased opacity of stratospheric hazes in neptune s atmosphere the deeper cloud structure and cloud composition of uranus and neptune would appear to be very similar

global prediction of abyssal hill root mean square heights from small scale altimetric gravity variability 1 abyssal hills which are pervasive landforms on the seafloor of the earth s oceans represent a potential tectonic record of the history of mid ocean ridge spreading however the most detailed global maps of the seafloor derived from the satellite altimetry based gravity field cannot be used to deterministically characterize such small scale 10 km morphology nevertheless the small scale variability of the gravity field can be related to the statistical properties of abyssal hill morphology using the upward continuation formulation in this paper i construct a global prediction of abyssal hill root mean square rms heights from the small scale variability of the altimetric gravity field the abyssal hill related component of the gravity field is derived by first masking distinct features such as seamounts mid ocean ridges and continental margins and then applying a newly designed adaptive directional filter algorithm to remove fracture zone discontinuity fabric a noise field is derived empirically by correlating the rms variability of the small scale gravity field to the altimetric noise field in regions of very low relief and the noise variance is subtracted from the small scale gravity variance suites of synthetically derived abyssal hill formed gravity fields are generated as a function of water depth basement rms heights and sediment thickness and used to predict abyssal hill seafloor rms heights from corrected small scale gravity rms height the resulting global prediction of abyssal hill rms heights is validated qualitatively by comparing against expected variations in abyssal hill morphology and quantitatively by comparing against actual measurements of rms heights although there is scatter the prediction appears unbiased

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

shear and richardson number in a mode water eddy abstract measurements of stratification and shear were carried out as part of the eddies tracer release experiment in mode water eddy a4 during the summer of 2005 these measurements were accomplished using both shipboard instrumentation and a drifting mooring a strong relationship between shear intensity and distance from the center of the eddy a4 was observed with the shipboard adcp diapycnal diffusivity at the sf6 tracer isopycnal prior to and during the release was estimated from the drifting mooring to be 2 9 10 6 m2 s 1 diffusivity increased by an order of magnitude to 3 2 10 5 m2 s 1 during the period of the final tracer survey in early september which was similar to the value estimated from the tracer analysis for the whole experiment 3 5 10 5 m2 s 1 ledwell j r mcgillicuddy jr d j anderson l a 2008 nutrient flux into an intense deep chlorophyll layer in a mode water eddy deep sea research ii this issue doi 10 1016 j dsr2 2008 02 005

methane depletion in both polar regions of uranus inferred from hst stis and keck nirc2 observations abstract from space telescope imaging spectrograph stis observations of uranus in 2012 when good views of its north polar regions were available we found that the methane volume mixing ratio declined from about 4 at low latitudes to about 2 at 60 80 n this depletion in the north polar region of uranus in 2012 is similar in magnitude and depth to that found in the south polar regions in 2002 this similarity is remarkable because of the strikingly different appearance of clouds in the two polar regions we have never seen any obvious signs of convective activity in the south polar region while the north has been peppered with numerous small clouds thought to be of convective origin keck and hubble space telescope imaging observations close to equinox at wavelengths of 1080 nm and 1290 nm with different sensitivities to methane and hydrogen absorption but similar vertical contribution functions imply that the depletions were simultaneously present in 2007 and at least their gross character is probably a persistent feature of the uranus atmosphere the depletion appears to be mainly restricted to the upper troposphere with the depth increasing poleward from about 30 n reaching 4 bars at 45 n and perhaps much deeper at 70 n where it is not well constrained by our observations the latitudinal variations in degree and depth of the depletions are important constraints on models of meridional circulation our observations are qualitatively consistent with previously suggested circulation cells in which rising methane rich gas at low latitudes is dried out by condensation and sedimentation of methane ice particles as the gas ascends to altitudes above the methane condensation level then is transported to high latitudes where it descends and brings down methane depleted gas since this cell would seem to inhibit formation of condensation clouds in regions where clouds are actually inferred from spectral modeling it suggests that sparse localized convective events may be important in cloud formation a more complex meridional circulation pattern may be necessary to reproduce the observed cloud distribution but microwave observations appear to be most compatible with a single deep circulation cell the small scale latitudinal variations we found in the effective methane mixing ratio between 55 n and 82 n have significant inverse correlations with zonal mean latitudinal variations in cloud reflectivity in near ir keck images taken before and after the hst observations if the ch4 h2 absorption ratio variations are interpreted as local variations in para fraction instead of methane mixing ratio we find that downwelling correlates with reduced cloud reflectivity while there has been no significant secular change in the brightness of uranus at continuum wavelengths between 2002 and 2012 there have been significant changes at wavelengths sensing methane and or hydrogen absorption with the southern hemisphere darkening considerably between 2002 and 2012 by 25 at mid latitudes near 827 nm for example while the northern hemisphere has brightened by 25 at mid latitudes at the same wavelength

volcanic growth faults and the origin of pacific abyssal hills the topographic features known as abyssal hills characterize 30 of the ocean floor and yet their origin has been the subject of vigorous debate for over 40 years submersible based investigations show that pacific abyssal hills are created on the flanks of the east pacific rise as horsts and grabens which lengthen with time hills are bounded on one side by ridge facing scarps produced by normal faulting and on the other by more gentle slopes produced by volcanic growth faulting

coordinated 1996 hst and irtf imaging of neptune and triton iii neptune s atmospheric circulation and cloud structure the first coordinated multispectral imaging of neptune and triton using both the hubble space telescope and the nasa infrared telescope facility in august 1996 l a sromovsky et al 149 416 434 435 458 provides new insights into neptune s atmospheric circulation and cloud structure from our 1996 data we derived cloud tracked winds for 18 features spanning latitudes from 61 s to 38 n finding generally close agreement with the smoothed 1989 voyager wind profile sromovsky et al 1993 icarus105 110 141 except for features associated with a northern great dark spot gds which moved with the spot rather than with the local mass flow providing another example of gds traveling companions in addition to finding a gds at 32 n thought to be the same one first seen in 1994 near the same latitude hammel et al 1995 science268 1740 1742 we also found a new kind of gds at 15 n which is unusual because of its low latitude and lack of a bright companion from blue images we determined that the dark cloud band near 60 s latitude is significantly nonaxisymmetric as was a similar band in 1989 voyager images both with a wavenumber one zonal structure and a 5 latitudinal variation we also identified a persistent pattern of clouds at 45 s which exhibit strong variations in brightness on yearly time scales using hst archived observations we determined cloud tracked winds for june and november 1994 and september 1995 confirming and extending the 1995 result of hammel and lockwood 1997 icarus129 466 481 that most winds agreed with the voyager profile a significant exception we found in november 1994 is the 100 m s meridional motion within the transient structure identified as the bright complex by h b hammel and g w lockwood 1997 icarus129 466 481 the integrated brightness of this group of gds traveling companions is sufficient to produce a hemispheric brightness asymmetry of 0 36 mag sromovsky et al 149 435 458 comparable to the 0 44 mag associated with the 1987 outburst maximum hammel et al 1992 icarus99 363 367 we determined spectral differences in cloud bands using complete global mosaics of 1996 imagery colocation of features in hst and groundbased near ir images enabled us to characterize spectral variations in discrete features from the visible to 2 4 m from which we estimated cloud heights for discrete bright features ranging from 60 to 230 mbars we found the equatorial atmosphere that is free of bright clouds to be very dark beyond 0 7 m from which we derived new upper bounds of 0 2 and 0 1 at 1 27 and 1 6 m respectively on the single scattering albedo of the putative 3 8 bar h2s cloud

tidal conversion at a submarine ridge the radiative flux of internal wave energy the tidal conversion powered by the oscillating flow of a uniformly stratified fluid over a two dimensional submarine ridge is computed using an integral equation method the problem is characterized by two nondimensional parameters a and b the first parameter a is the ridge half width scaled by h where h is the uniform depth of the ocean far from the ridge and is the inverse slope of internal tidal rays horizontal run over vertical rise the second parameter b i s the ridge height scaled by h two topographic profiles are considered a triangular or tent shaped ridge and a polynomial ridge with continuous topographic slope for both profiles complete coverage of the a b parameter space is obtained by reducing the problem to an integral equation which is then discretized and solved numerically it is shown that in the supercritical regime ray slopes steeper than topographic slopes the radiated power increases monotonically with b and decreases monotonically with a in the subcritical regime the radiated power has a complicated and nonmonotonic dependence on these parameters as a 0 recent results are recovered for the tidal conversion produced by a knife edge barrier it is shown analytically that the a 0 limit is regular if a 1 the reduction in tidal conversion below that at a 0 is proportional to a 2 further the knife edge model is shown to be indicative of both conversion rates and the structure of the radiated wave field over a broad region of the supercritical parameter space as a increases the topographic slopes become gentler and at a certain value of a the ridge becomes critical that is there is a single point on the flanks at which the topographic slope is equal to the slope of an internal tidal beam the conversion decreases continuously as a increases through this transition visualization of the disturbed buoyancy field shows prominent singular lines tidal beams in the case of a triangular ridge these beams originate at the crest of the triangle in the case of a supercritical polynomial ridge the beams originate at the shallowest point on the flank at which the topographic slope equals the ray slope

saturation of the internal tides and induced mixing in the abyssal ocean as part of an ongoing effort to develop a parameterization of wave induced abyssal mixing the authors derive an heuristic model for nonlinear wave breaking and energy dissipation associated with internal tides then the saturation and dissipation of internal tides for idealized and observed topography samples are investigated one of the main results is that the wave induced mixing could be more intense and more confined to the bottom than previously assumed in numerical models furthermore in this model wave breaking and mixing clearly depend on the small scales of the topography below 10 km or so which is below the current resolution of global bathymetry this motivates the use of a statistical approach to represent the unresolved topography when addressing the role of internal tides in mixing the deep ocean

internal tide dissipation mixing and vertical nitrate flux at the shelf edge of ne new zealand an internal tide on the ne shelf of new zealand was observed with a combination of moored temperature loggers and current meters and vertical profiling with a microstructure probe internal tide energy flux across the shelf edge was calculated to be 400 w m with considerable variability driven by the passage of a storm through the region energy associated with the internal tide was significantly greater than the energy of the barotropic tide or of inertial shear dissipation of the internal tide calculated from the energy loss between two of the moorings was estimated to be 15 10 mw m 2 the associated vertical eddy diffusivity was 4 3 x 10 4 m 2 s 1 the microstructure observations indicated internal tide driven vertical diffusivities at the nitracline of 7 x 10 4 m 2 s 1 the observations of vertical eddy diffusivities are combined with measurements of the vertical nitrate gradient to suggest that mixing driven by the internal tide is the dominant mechanism for driving diapycnal nutrient supply during summer the calculated flux of about 12 mmol n m 2 d 1 into the photic zone is suggested to drive significant new subsurface production throughout the summer amounting to a possible contribution to annual new production on the shelf of 100 g c m 2

statistical characterization of geosat altimetry noise dependence on environmental parameters 1 sea surface height ssh measurements from the geosat satellite altimetry mission are analyzed to statistically characterize their noise process which is defined here as the small scale 50 km time varying component of the altimetry data this analysis is one component of a larger effort to extract meaningful information about seafloor roughness from the small scale fabric of the altimetric gravity field both small scale seafloor topography e g abyssal hills and ssh noise significantly influence the measured gravity fabric hence a global quantitative understanding of ssh noise is required to infer what portion of the gravity fabric is associated with the true geoid it is also anticipated that the ssh noise analysis will prove useful in designing improvements to altimetry processing algorithms the ssh data are first processed by differencing nearest neighbor tracks to minimize the static component of variability and then by high pass filtering to remove variability associated with mesoscale oceanic circulation autocovariance analysis reveals that ssh noise can be decomposed into uncorrelated white noise and correlated semiperiodic components three parameters are measured which characterize the variance of both components and the correlation length of the correlated component the global distribution of uncorrelated noise variance is closely correlated to significant wave heights directly linking the uncertainty of the altimeter return time to the roughness of the sea surface the variance and correlation length of the correlated component of noise can be associated with three separate environmental parameters sea ice precipitation rates and upper atmospheric variability associated with the subtropical jet stream as widely differing as these environmental processes are it is hypothesized that features like sea ice rain storms and atmospheric turbulence can cause sudden perturbations in the return time of the altimetry signal creating decaying oscillations associated with the onboard tracking algorithms

uranus in 2003 zonal winds banded structure and discrete features abstract imaging of uranus in 2003 with the keck 10 m telescope reveals banded zonal structure and dozens of discrete cloud features at j and h bands several features in the northern hemisphere are also detectable at k by tracking features over four days we extend the zonal wind profile well into the northern hemisphere we report the first measurements of wind velocities at latitudes 13 19 and northward of 43 the first direct wind measurements near the equator and the highest wind velocity seen yet on uranus 218 m s at northern mid latitudes 20 to 40 the winds appear to have accelerated when compared to earlier hst and keck observations southern wind speeds 20 to 43 have not changed since voyager measurements in 1986 the equator of uranus exhibits a subtle wave structure indicated by diffuse patches roughly every 30 in longitude the largest discrete cloud features on uranus show complex structure extending over tens of degrees reminiscent of activity seen around neptune s great dark spot during the voyager encounter with that planet there is no sign of a northern polar collar as is seen in the south but a number of discrete features seen at the expected latitudes may signal the early stages of development of a northern collar

mixing on the continental slope of the southern weddell sea shipboard hydrography and current profiles collected in 2003 and time series from moored current meters deployed in late 1990s are analyzed to study the variability of mixing in the southeastern weddell sea profiles of eddy diffusivity k are inferred from finescale shear vertical derivative of horizontal velocity and strain vertical derivative of isopycnal displacement variance using parameterizations which relate the internal wave energy to the dissipation rate at small scales the highest mixing rates are seen near the bottom where the eddy diffusivities are elevated by one order of magnitude from those in the interior and exceed 10 4 m 2 s 1 the observations show latitudinal variability in k particularly near the bottom where k significantly increases near 74 28 s the critical latitude for lunar semi diurnal m2 tides in this region the critical latitude coincides with near critical topography on the upper continental slope a situation which favors generation of m2 internal waves consistent with the results from finescale shear and strain parameterizations which indicate highest bottom diffusivities near the critical latitude independent analysis of current time series from moored instruments shows a thickening of the frictional bottom boundary layer near the critical latitude semidiurnal tidal dynamics at the upper continental slope together with the critical latitude effects lead to mixing that might significantly affect the regional heat budget and the circulation in the study area

stochastic modeling of seafloor morphology a parameterized gaussian model stochastic methods of analysis are useful for quantifying ensemble properties of small scale bathymetric features such as abyssal hills in this paper we model the seafloor as a stationary zero mean gaussian random field completely specified by its autocovariance function we formulate an anisotropic autocovariance function that has five free parameters describing the amplitude anisotropic orientation and aspect ratio characteristic length and hausdorff fractal dimension of seafloor topography parameters estimated from various seafloor regions by an inversion of sea beam data indicate that the seafloor exhibits a wide range of stochastic characteristics within the constraints of the model synthetic topography can be generated at arbitrary scale and resolution from the gaussian model using a fourier method color images of these synthetics are useful for illustrating the stochastic behavior of the model

the role of internal tides in mixing the deep ocean abstract internal wave theory is used to examine the generation radiation and energy dissipation of internal tides in the deep ocean estimates of vertical energy flux based on a previously developed model are adjusted to account for the influence of finite depth varying stratification and two dimensional topography specific estimates of energy flux are made for midocean ridge topography weakly nonlinear theory is applied to the wave generation at idealized topography to examine finite amplitude corrections to the linear theory most internal tide energy is generated at low modes associated with spatial scales from roughly 20 to 100 km the richardson number of the radiated internal tide typically exceeds unity for these motions and so direct shear instability of the generated waves is not the dominant energy transfer mechanism it also seems that wave wave interactions are ineffective at transferring energy from the large wavelengths that dominate the energy flux instead it appears that most of

tides and the climate some speculations abstract the important role of tides in the mixing of the pelagic oceans has been established by recent experiments and analyses the tide potential is modulated by long period orbital modulations previously loder and garrett found evidence for the 18 6 yr lunar nodal cycle in the sea surface temperatures of shallow seas in this paper the possible role of the 41 000 yr variation of the obliquity of the ecliptic is considered the obliquity modulation of tidal mixing by a few percent and the associated modulation in the meridional overturning circulation moc may play a role comparable to the obliquity modulation of the incoming solar radiation insolation a cornerstone of the milankovic theory of ice ages this speculation involves even more than the usual number of uncertainties found in climate speculations

tidal conversion by supercritical topography calculations are presented of the rate of energy conversion of the barotropic tide into internal gravity waves above topography on the ocean floor the ocean is treated as infinitely deep and the topography consists of periodic obstructions a green function method is used to construct the scattered wavefield the calculations extend the previous results of balmforth et al for subcritical topography wherein waves propagate along rays whose slopes exceed that of the topography everywhere by allowing the obstacles to be arbitrarily steep or supercritical so waves propagate at shallower angles than the topographic slopes and are scattered both up and down a complicated pattern is found for the dependence of energy conversion on e the ratio of maximum topographic slope to wave slope and the ratio of obstacle amplitude and separation this results from a sequence of constructive and destructive interferences between scattered waves that has implications for computing tidal conversion rates for the global ocean

voyager 2 in the uranian system imaging science results voyager 2 images of the southern hemisphere of uranus indicate that submicrometersize haze particles and particles of a methane condensation cloud produce faint patterns in the atmosphere the alignment of the cloud bands is similar to that of bands on jupiter and saturn but the zonal winds are nearly opposite at mid latitudes 70 degrees to 27 degrees where winds were measured the atmosphere rotates faster than the magnetic field however the rotation rate of the atmosphere decreases toward the equator so that the two probably corotate at about 20 degrees voyager images confirm the extremely low albedo of the ring particles high phase angle images reveal on the order of 10 2 new ringlike features of very low optical depth and relatively high dust abundance interspersed within the main rings as well as a broad diffuse low optical depth ring just inside the main rings system nine of the newly discovered small satellites 40 to 165 kilometers in diameter orbit between the rings and miranda the tenth is within the ring system two of these small objects may gravitationally confine the e ring oberon and umbriel have heavily cratered surfaces resembling the ancient cratered highlands of earth s moon although umbriel is almost completely covered with uniform dark material which perhaps indicates some ongoing process titania and ariel show crater populations different from those on oberon and umbriel these were probably generated by collisions with debris confined to their orbits titania and ariel also show many extensional fault systems ariel shows strong evidence for the presence of extrusive material about halfof miranda s surface is relatively bland old cratered terrain the remainder comprises three large regions of younger terrain each rectangular to ovoid in plan that display complex sets of parallel and intersecting scarps and ridges as well as numerous outcrops of bright and dark materials perhaps suggesting some exotic composition

a global and regional stochastic analysis of near ridge abyssal hill morphology this paper presents the results of a global and regional stochastic analysis of near ridge abyssal hill morphology the analysis includes the use of sea beam data for the estimation of stochastic parameters up to order 4 these parameters provide important quantitative physical information regarding abyssal hills including their rms height azimuthal orientation characteristic width aspect ratio hausdorff dimension skewness tilt and peakiness the global data set consists of 64 sea beam swaths near the rivera cocos and nazca spreading sections of the east pacific rise the mid atlantic ridge and the central indian ridge in one form of analysis the parameters are averaged among spreading rate bins each of the spreading rate subsets can be identified as unique from the others in at least one aspect the slowest spreading rate subset mid atlantic data exhibit the largest scales rms height and characteristic width and length of abyssal hills these parameters generally decrease as spreading rate increases up to the fast spreading rate data pacific cocos but increase going from fast to very fast pacific nazca spreading rate data this indicates some complexity in the relationship between spreading rate and abyssal hill morphology the plan view aspect ratio is nearly twice as large for the fast spreading rate data than for any of the other subsets and is smallest for the very fast spreading rate data the fractal dimension is nearly identical for all spreading rate subsets the vertical skewness is positive for the slow and medium spreading rate data indicating larger peaks than troughs and negative for the fast spreading rate data indicating larger troughs than peaks the kurtosis or peakiness is everywhere larger than the gaussian value of 3 and tends to be larger in the atlantic than the pacific the tilting parameter provides substantial evidence indicating steeper inward facing slopes in the medium and fast spreading rate data but only marginal evidence for it in the slow spreading rate data from an analysis of correlations among parameters it is found that subsets sometimes behave differently from the entire data set in particular while over the global data set the characteristic width exhibits a well resolved positive trend when plotted versus rms height these parameters exhibit a more gradual positive trend in the mid atlantic data and a negative trend in the pacific cocos data in addition the plan view aspect ratio while generally uncorrelated with rms height for the global data set is positively correlated with rms height for the pacific cocos data set these results emphasize a strong uniqueness of the pacific cocos data relative to the rest of the data global set the pacific cocos data consist of 27 swaths concentrated between the siquieros and orozco fracture zones these data provide very good abyssal hill coverage of this well mapped and well studied region and form the basis of a regional analysis of the correlation between ridge morphology and stochastic abyssal hill parameters in this analysis it is found that abyssal hill parameters are correlated with the depth of the adjacent ridge axis indicating that the relative abundance in magma supply which likely controls the ridge axis depth may also be an important influence on the formation of abyssal hills

effect of landfast sea ice on coastal currents driven by the wind the present study examines the effects of landfast sea ice on the response of a homogeneous coastal ocean to wind forcings under the longwave approximation for a fluctuating wind continental shelf waves are induced by an infinite stress curl due to the existense of the ice edge as well as by the torque due to the topographic change the amplitude and sign of each shelf wave mode excited by the forcing depend strongly on the ice edge location the alongshore velocity field which can be represented as the sum of all the shelf wave modes has a maximum in amplitude at the ice edge with a strong lateral shear which is a result of the infinite stress curl the amplitudes of alongshore velocity and sea level near the coast are greatly reduced as the ice edge advances the response to a steady wind is also examined and it is found that even for the same wind the velocity distributions depend strongly on the ice edge location for instance the current direction near the coast is the same as that of the wind stress in the case of no fast ice whereas it is opposite in the case where the ice edge is located at the shelf break the present theory is applied to the continental shelf off enderby land antarctica and it gives the possible explanation for the observed features that the current variability its coherence with the wind and the prevailing current direction depend much on the extent of landfast sea ice

bathymetric prediction from dense satellite altimetry and sparse shipboard bathymetry the southern oceans south of 30 s are densely covered with satellite derived gravity data track spacing 2 4 km and sparsely covered with shipboard depth soundings hundreds of kilometers between tracks in some areas flexural isostatic compensation theory suggests that bathymetry and downward continued gravity data may show linear correlation in a band of wave lengths 15 160 km if sediment cover is thin and seafloor relief is moderate at shorter wave lengths the gravity field is insensitive to seafloor topography because of upward continuation from the seafloor to the sea surface at longer wavelengths isostatic compensation cancels out most of the gravity field due to the seafloor topography we combine this theory with wiener optimization theory and empirical evidence for gravity noise to signal ratios to design low pass and band pass filters to use in predicting bathymetry from gravity the prediction combines long wavelengths 160 km from low pass filtered soundings with an intermediate wavelength solution obtained from multiplying downward continued band pass filtered 15 160 km gravity data by a scaling factor s s is empirically determined from the correlation between gravity data and existing soundings in the 15 160 km band by robust regression and varies at long wave lengths we find that areas with less than 200 m of sediment cover show correlation between gravity and bathymetry significant at the 99 level and s may be related to the density of seafloor materials in these areas the prediction has a horizontal resolution limit of 5 10 km in position and is within 100 m of actual soundings at 50 of grid points and within 240 m at 80 of these in areas of very rugged topography the prediction underestimates the peak amplitudes of seafloor features images of the prediction reveal many tectonic features not seen on any existing bathymetrie charts because the prediction relies on the gravity field at wavelengths 160 km it is insensitive to errors in the navigation of sounding lines but also cannot completely reproduce them therefore it may be used to locate tectonic features but should not be used to assess hazards to navigation the prediction is available from the national geophysical data center in both digital and printed form

semi diurnal and diurnal tidal dissipation from topex poseidon altimetry 1 tidal energy dissipation is estimated for eight semi diurnal and diurnal constituents using a global inverse solution constrained by topex poseidon altimeter data very similar spatial patterns are obtained for all semi diurnal constituents with about one third of the total dissipation occurring in the deep ocean over rough topography maps for diurnal constituents are also similar amongst themselves but quite different from the semi diurnal results for diurnals a smaller fraction of dissipation roughly 10 occurs in the deep ocean much of the difference can be explained by the very different spatial pattern of diurnal and semi diurnal tidal currents the lack of free internal waves at frequencies poleward of 30 at diurnal frequencies also probably plays a role limiting the effectiveness of baroclinic conversion as an energy sink for barotropic diurnal tides

estimates of m2 tidal energy dissipation from topex poseidon altimeter data most of the tidal energy dissipation in the ocean occurs in shallow seas as has long been recognized however recent work has suggested that a significant fraction of the dissipation perhaps 1 tw or more occurs in the deep ocean this paper builds further evidence for that conclusion more than 6 years of data from the topex poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean the dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence computed using currents derived by least squares fitting of the altimeter data and the shallow water equations such calculations require dynamical assumptions in particular about the nature of dissipation to assess sensitivity of dissipation estimates to input assumptions a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared these experiments and monte carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates owing to the tight constraints on tidal elevation fields provided by the altimeter area integrals of the energy balance are remarkably insensitive to required dynamical assumptions tidal energy dissipation is estimated for all major shallow seas excluding individual polar seas and compared with previous model and data based estimates dissipation in the open ocean is significantly enhanced around major bathymetric features in a manner consistent with simple theories for the generation of baroclinic tides

clouds and aerosols on uranus radiative transfer modeling of spatially resolved near infrared keck spectra abstract we observed uranus in the near infrared h and k bands 1 47 2 38 m in 2010 and 2011 with the osiris imaging spectrograph on the keck ii telescope with adaptive optics in 2010 three years past the equinox we had a good view of the north polar region while still having access to southern latitudes down to 70 s in 2011 our observations focused on a moderately bright discrete cloud feature in the middle of the bright circumpolar band at 45 n the spatial and spectral resolution of our data allow us to retrieve atmospheric parameters between 65 s and 75 n via radiative transfer modeling we test vertical aerosol profiles with combinations of diffuse and compact scattering layers and find that we can reproduce our equatorial data for a range of cases provided the deepest detectable aerosol layer is compact and located between 2 and 3 bars with the higher cloud altitudes corresponding to models with higher methane deep volume mixing ratios using a parameterized atmosphere with a diffuse upper haze and a moderately compact lower cloud we find that both the haze and the cloud reach their maximal optical depth just north of the equator and thin toward the poles when we fix the abundance of methane with latitude we find that the bottom cloud shifts to shallower depths at higher latitudes in both hemispheres for a methane profile with a deep volume mixing ratio of 2 22 the cloud rises from the 3 bar level equatorward of 20 to above 2 bars by 60 however when we allow the tropospheric methane abundance to vary according to a parameterized vertical profile we find that the lower cloud depth is stable in latitude while the methane becomes increasingly depleted toward both poles in both cases we find denser aerosol layers and higher methane abundances in the northern hemisphere than the southern consistent with a seasonal post equinox trend in particular the bright band near 45 n is relatively undepleted in methane and represents a local peak in the opacity and altitude of the lower cloud the cloud feature we detected in 2011 falls in the middle of this band this feature extends from a depth of 1 3 bars up to the 0 5 bar level both ch4 and h2s are expected to condense below this level if the cloud has formed as the result of a convective upwelling event these are the most likely condensation species

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

observations of turbulence caused by a combination of tides and mean baroclinic flow over a fjord sill thisstudyinvestigates thedissipation ratesandflow conditionsatthedrobaksillinthe oslofjord thearea was transected 13 times with a free falling microstructure shear probe during 4 days in june 2011 at the same time an adcp was deployed inside the sill during most tidal cycles internal hydraulic jumps with high dissipation rates were foundon the downstreamside of the sill however the internal responsevariedstrongly betweendifferenttidal cycleswith similar barotropicforcing in the beginning of the observational period ebb tides had no hydraulic jumps and in the end one of the flood tides did not have a hydraulic jump during the same period the mean baroclinic exchange flow changed from inflow to outflow in the bottom layer the authors conclude that the conditions at the sill are on the edge of forming hydraulic jumps and that the mean baroclinic exchange may push the flow above or below the limit of a hydraulic jump depending on the situation this conclusion is supported by two layer hydraulic theory the volume integrated dissipation rates within 500m from the sill crest compare well with estimates of energy loss in the lower layer calculated from the bernoulli drop under the assumption of no energy loss in the upper layer finally the mean dissipation rateatthesillwascomparedwiththeradiationofinternaltidalenergyawayfromthesill anditwasfoundthat about 60 90 of the total energy loss was dissipated locally

post equinox observations of uranus berg s evolution vertical structure and track towards the equator we present observations of uranus taken with the near infrared camera nirc2 on the 10 m w m keck ii telescope the wide field planetary camera 2 wfpc2 and the wide field camera 3 wfc3 on the hubble space telescope hst from july 2007 through november 2009 in this paper we focus on a bright southern feature referred to as the berg in sromovsky et al sromovsky l a fry p m hammel h b ahue a w de pater i rages k a showalter m r van dam m 2009 icarus 203 265 286 we reported that this feature which oscillated between latitudes of 32 and 36 for several decades suddenly started on a northward track in 2005 in this paper we show the complete record of observations of this feature s track towards the equator including its demise after an initially slow linear drift the feature s drift rate accelerated at latitudes 25 by late 2009 the feature very faint by then was spotted at a latitude of 5 before disappearing from view during its northward track the feature s morphology changed dramatically and several small bright unresolved features were occasionally visible poleward of the main streak these small features were sometimes visible at a wavelength of 2 2 m indicative that the clouds reached altitudes of 0 6 bar the main part of the berg which is generally a long sometimes multipart streak is estimated to be much deeper in the atmosphere near 3 5 bars in 2004 but rising to 1 8 2 5 bars in 2007 after it began its northward drift through comparisons with neptune s great dark spot and simulations of the latter we discuss why the berg may be tied to a vortex an anticyclone deeper in the atmosphere that is visible only through orographic companion clouds

a tracer study of mixing in the santa cruz basin a tracer release experiment to study diapycnal and isopycnal mixing was performed in santa cruz basin in 1988 1989 approximately 1450 g of sulfur hexafluoride were injected close to an isopycnal surface at 1500 m depth in may 1988 this depth is midway between the bottom of the basin at 1920 m and the sill at 1084 m the diapycnal dispersion measured during the first few months while the tracer was still mixing to the walls of the basin yielded a diapycnal eddy diffusivity of 1 0 cm2 s 1 within a factor of 1 5 this is approximately 4 times larger than the diffusivity found by ledwell and watson 1991 in the interior of santa monica basin where the buoyancy frequency was 5 times greater the tracer was well mixed to the walls 6 months after the injection and at that time the diapycnal spread of the tracer was greater near the walls than in the interior the rate of diapycnal dispersion of the tracer increased dramatically after the tracer had mixed to the walls of the basin indicating enhanced boundary mixing an effective basin wide diapycnal diffusivity of 10 cm2 s 1 would be required to support the fluxes of tracer observed a one dimensional model for tracer and heat diffusion does not simulate the results very well however probably because of the finite mixing time between the boundary region and interior and because of the complexity of the processes in the boundary region

evidence for enhanced mixing over rough topography in the abyssal ocean the overturning circulation of the ocean plays an important role in modulating the earth s climate but whereas the mechanisms for the vertical transport of water into the deep ocean deep water formation at high latitudes and horizontal transport in ocean currents have been largely identified it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise however measurements of the internal wave field the main source of energy for mixing and of turbulent dissipation rates have typically implied diffusivities across surfaces of equal density of only approximately 0 1 cm2 s 1 too small to account for the return flow here we report measurements of tracer dispersion and turbulent energy dissipation in the brazil basin that reveal diffusivities of 2 4 cm2 s 1 at a depth of 500 m above abyssal hills on the flank of the mid atlantic ridge and approximately 10 cm2 s 1 nearer the bottom this amount of mixing probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry may be large enough to close the buoyancy budget for the brazil basin and suggests a mechanism for closing the global overturning circulation

epic simulations of bright companions to neptune s great dark spots abstract we present a three dimensional model of the bright companion clouds associated with neptune s great dark spots gdss our results support the hypothesis that the bright companions of the southern hemisphere gds discovered in 1989 and of the northern hemisphere gds discovered in 1994 are methane clouds that form at or just below the tropopause and that they are caused by lifting in a manner analogous to the formation of orographic clouds we vary the vertical position of the gds and find that the companion cloud is a robust feature except when the anticyclone itself does not survive when a gds is started with its top in the stratosphere it drifts much too rapidly toward the equator and quickly disperses on the other hand if its top is well below the tropopause there is a tendency for the companion clouds to be too large hence the top of a gds is probably at the tropopause along an open streamline that threads a bright companion the typical pressure and temperature drops are about 3 mb and 1k respectively corresponding to a lift of about half a kilometer or 4 of the pressure scale height and the relative horizontal wind speed is about 45 m s 1 eastward through the cloud

a mechanism for local dissipation of internal tides generated at rough topography abstract fine and micro structure observations indicate that turbulent mixing is enhanced within o 1 km above rough topography enhanced mixing is associated with internal wave breaking and in many regions of the ocean has been linked to the breaking and dissipation of internal tides the generation and dissipation of internal tides are explored in this study using a high resolution two dimensional nonhydrostatic numerical model which explicitly resolves the instabilities leading to wave breaking configured in an idealized domain with a realistic multiscale topography and flow characteristics the control simulation chosen to represent the brazil basin region produces a vertical profile of energy dissipation and temporal characteristics of finescale motions that are consistent with observations results suggest that a significant fraction of mixing in the bottom o 1 km of the ocean is sustained by the transfer of energy from the large scale internal tides to smaller scale internal waves by nonlin

internal wave induced dispersion and mixing on a sloping boundary 1 a fluorescent dye tracer was released in a stratified water column above a sloping boundary revealing profound dispersive asymmetry initially the dye spread symmetrically in the vertical until the deeper portion became influenced by the bottom boundary layer bbl the shallower portion then spread rapidly up slope in a thin boundary layer influenced by highly non linear isopycnal distortions the deeper down slope portion of dye subsequently became detached from the boundary and intruded into the basin interior in three distinct layers along isopycnal surfaces the intrusions result from the gravitational collapse of mixing patches created by baroclinic flow over an irregular boundary the vertical separation of the layers matches the inverse topographic wavenumber up slope displacement of the dye is consistent with an advective diffusive balance near the sloping boundary controlled by slope angle and roughness horizontal diffusivities increased from 1 4 m2s 1 to 18 4 m2s 1 during the 4 day experiment

mixing coefficient in stably stratified flows abstractturbulent mixing in the interior of the oceans is not as well understood as mixing in the oceanic boundary layers mixing in the generally stably stratified interior is primarily although

dynamics of wind driven upwelling and relaxation between monterey bay and point arena local regional and gyre scale controls 1 in north and central california equatorward winds drive equatorward flows and the upwelling of cold dense water over the shelf during the midspring and summer upwelling season when the winds temporarily weaken the upwelling flows between point reyes and point arena relax becoming strongly poleward over the shelf analytical and numerical models are used to describe the effect of alongshore variability of winds bathymetry and basin scale pressure gradients on the strength of upwelling and its relaxation alongshore winds weaken to the south of point reyes and the shelf becomes narrower from point reyes to monterey bay both of these lead to reduced upwelling at and to the north of point reyes causing an alongshore gradient of temperature and density on the shelf these alongshore gradients lead to an along isobath pressure gradient over the shelf that drive the relaxation flows a simple analytical model is used to explain the dynamics magnitude and structure of the relaxation flows the modeling also suggests that the depth of origin of the upwelled waters and thus their temperature is controlled by the along isobath pressure gradient that exists over the continental slope this along slope pressure gradient is also responsible for the california undercurrent in this region this pressure gradient is not generated in a model of the californian coast extending from 32 n to 42 n and integrated for several months suggesting it is caused by dynamics whose spatial or temporal scales are larger than the californian coast and or longer than several months

determination of diapycnal diffusion rates in the upper thermocline in the north atlantic ocean using sulfur hexafluoride 1 the apparent diapycnal diffusivity below the wind driven surface mixed layer of the ocean was determined in an anticyclonic eddy in the eastern north atlantic using sulfur hexafluoride sf6 tracer data collected in june 1998 in this tracer experiment the downward penetration of sf6 was measured for 3 weeks following the deliberate injection of sf6 in the surface mixed layer the resulting data were used to constrain the one dimensional fickian diffusion model to estimate the diapycnal diffusivity the model also includes the lateral diffusion component so that it can more accurately represent the time evolution of the sf6 concentrations along the isopycnal surface this affects the estimation of the diapycnal diffusivity for the upper thermocline immediately below the surface mixed layer we estimated the diapycnal diffusivity for the 3 week period as 0 3 0 2 cm2 s 1 at a buoyancy frequency of 8 2 cph

vertical aerosol structure of neptune constraints from center to limb profiles abstract we present and analyze center to limb ctl profiles of the equatorial region of neptune extracted from images with good spatial resolution models of the quiescent atmosphere of neptune are consistent with at least two distinct cloud layers a thin stratospheric haze and a deep cloud the 8900 a ctl profile requires the presence of some material above the 5 mbar level assuming isotropic scattering the optical depth of the material is less than 0 15 for hazes with single scattering albedos larger than 0 6 ctl profiles at three methane bands could not be fitted simultaneously with a single scattering layer implying that there may be multiple haze layers the methane band data tolerate thin scattering hazes in the pressure level from 0 4 to 1 5 bars but the optical depths must be less than 0 05 again assuming isotropic scattering such a thin haze does not provide sufficient reflected flux at 6340 a a continuum region indicating the presence of another scattering layer deeper than 1 5 bars a bright cloud layer single scattering albedo near 1 with optical depth 3 0 at 2 6 bars provides a good fit to 6340 a reflectivity superposed on the quiescent atmosphere are discrete bright features the lack of detectable disk integrated variability at shorter wavelengths helps constrain the vertical aerosol structure of these bright regions specifically the difference of the bright feature from its surroundings in 1986 was probably caused by an increase in optical depth or height of a stratospheric haze layer

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

mixing of a tracer in the pycnocline a patch of sulfur hexafluoride was released in may 1992 in the eastern north atlantic on an isopycnal surface near 300 m depth and was surveyed over a period of 30 months as it dispersed across and along isopycnal surfaces the diapycnal eddy diffusivity k estimated for the first 6 months was 0 12 0 02 cm2 s while for the subsequent 24 months it was 0 17 0 02 cm2 s the vertical tracer distribution remained very close to gaussian for the full 30 months as the root mean square rms dispersion grew from 5 to 50 m lateral dispersion was measured on several scales the growth of the rms width of the tracer streaks from less than 100 m to approximately 300 m within 2 weeks implies an isopycnal diffusivity of 0 07 m2 s at scales of 0 1 to 1 km larger than expected from the interaction between vertical shear of the internal waves and diapycnal mixing teasing of the overall patch initially about 25 km across into streaks with an overall length of 1800 km within 6 months supports predictions of exponential growth by the mesoscale strain field at a rate of 3 0 5 10 7 s 1 the rms width of these streaks estimated as 3 km and maintained in the face of the streak growth indicates an isopycnal diffusivity of 2 m2 s at scales of 1 to 10 km much greater than expected from internal wave shear dispersion the patch was painted in albeit streakily by 12 months confirming expectations from analytical and numerical models homogenization of the patch continued during the subsequent 18 months while the patch continued to spread with an effective isopycnal eddy diffusivity on the order of 1000 m2 s acting at scales of 30 to 300 km

global estimates of seafloor slope from single beam ship soundings 1 rough topography on the ocean floor is a source of ocean mixing which is of interest to both physical oceanography and climate science most mixing has been attributed to high slopes of the large scale structures of the deep ocean floor such as seamounts continental margins and mid ocean ridge axes in this paper we show the small scale but ubiquitous abyssal hills and fracture zones dominate the global map of rough topography much of this rugged seafloor occurs in the southern ocean on the flanks of the pacific antarctic rise and southwest indian ridge we present our results as a global map of the mean slope of the ocean floor and as a global map of the ocean floor above them2 critical slope we compare our results to multibeam and satellite bathymetry data to show that satellite bathymetry is not a valid proxy for multibeam measurements but edited single beam sonar data are adequate to provide a global perspective on features with horizontal wavelengths as small as 2 km

the role of bottom pressure torques on the interior pathways of north atlantic deep water abstractfour versions of the same global climate model one with horizontal resolution of 1 8 3 6 and three with 0 2 0 4 are employed to evaluate the role of ocean bottom topography and viscosity on the spatial structure of the deep circulation this study is motivated by several recent observational studies that find that subsurface floats injected near the western boundary of the labrador sea most often do not continuously follow the deep western boundary current dwbc in contrast to the traditional view that the deep water formed in the north atlantic predominantly follows the dwbc it is found that with imposed large viscosity values the model reproduces the traditional view however as viscosity is reduced and the model bathymetry resolution increased much of the north atlantic deep water nadw separates from the western boundary and enters the low latitude atlantic via interior pathways distinct from the dwbc it is shown that bottom pressure torques play an important role in maintai

significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data how and where the ocean tides dissipate their energy are long standing questions1 that have consequences ranging from the history of the moon2 to the mixing of the oceans3 historically the principal sink of tidal energy has been thought to be bottom friction in shallow seas4 5 there has long been suggestive evidence6 7 however that tidal dissipation also occurs in the open ocean through the scattering by ocean bottom topography of surface tides into internal waves but estimates of the magnitude of this possible sink have varied widely3 8 9 10 11 here we use satellite altimeter data from topex poseidon to map empirically the tidal energy dissipation we show that approximately 1012 watts that is 1 tw representing 25 30 of the total dissipation occurs in the deep ocean generally near areas of rough topography of the estimated 2 tw of mixing energy required to maintain the large scale thermohaline circulation of the ocean12 one half could therefore be provided by the tides with the other half coming from action13 on the surface of the ocean

analysis of neptune s 2017 bright equatorial storm abstract we report the discovery of a large 8500 km diameter infrared bright storm at neptune s equator in june 2017 we tracked the storm over a period of 7 months with high cadence infrared snapshot imaging carried out on 14 nights at the 10 m keck ii telescope and 17 nights at the shane 120 inch reflector at lick observatory the cloud feature was larger and more persistent than any equatorial clouds seen before on neptune remaining intermittently active from at least 10 june to 31 december 2017 our keck and lick observations were augmented by very high cadence images from the amateur community which permitted the determination of accurate drift rates for the cloud feature its zonal drift speed was variable from 10 june to at least 25 july but remained a constant 237 4 0 2 m s 1 from 30 september until at least 15 november the pressure of the cloud top was determined from radiative transfer calculations to be 0 3 0 6 bar this value remained constant over the course of the observations multiple cloud break up events in which a bright cloud band wrapped around neptune s equator were observed over the course of our observations no dark spot vortices were seen near the equator in hst imaging on 6 and 7 october the size and pressure of the storm are consistent with moist convection or a planetary scale wave as the energy source of convective upwelling but more modeling is required to determine the driver of this equatorial disturbance as well as the triggers for and dynamics of the observed cloud break up events

near boundary mixing above the flanks of a midlatitude seamount fine scale velocity and density profile data with concurrent turbulent velocity and temperature dissipation estimates obtained above the flanks of fieberling guyot a seamount in the eastern north pacific ocean are examined for evidence of near bottom boundary mixing fine scale shear and strain spectral levels were elevated over the flanks of the seamount in a 500 m thick stratified layer above the bottom the velocity shear was horizontally isotropic clockwise and counterclockwise with depth shear spectral levels were comparable and no significant correlation between shear and strain was observed above the steepest bottom slopes near the seamount summit rim excess vertical strain relative to shear was observed as compared to the background internal wave field suggesting the presence of high frequency internal waves these signals may have been the product of wave reflections from the steep flanks of the seamount and or wave generation from tidal currents flowing over the rough bottom associated with the enhanced shears and strains were more frequent occurrences of low 10 m richardson number events increased overturning scales and larger estimated turbulent eddy diffusivity relative to observations 15 km or more from the seamount in particular turbulent diffusivity estimates increased from o 0 1 10 4 m2 s 1 in the ocean interior to 1 5 10 4 m2 s 1 within 500 m vertically 1 3 km horizontally of the seamount flank a simple geometric scaling argument suggests that boundary mixing of this intensity has relevance to the large scale circulation at abyssal depths where a large fraction of the ocean waters is in close proximity to the bottom

habitat characterization of the vema fracture zone and puerto rico trench abstract although many of the regions on and close to the mid ocean ridges have been extensively mapped and sampled the abyssal intraplate regions remain essentially unsampled and unmapped leaving huge gaps in our understanding of their geologic history and present activity prominent bathymetric features in these intraplate regions are fracture zones here we present bathymetric and sampling information from a transatlantic transect along the vema fracture zone ca 11 n covering crustal ages from 109 0 ma on the african plate and 0 62 ma on the south american plate the vema fracture zone is the intraplate trace of the active vema transform plate boundary which offsets the present day mid atlantic ridge by ca 300 km left laterally juxtaposing zero age crust with crust of 20 million years age our results show clear evidence of tectonic activity along most of the fracture zone in most places likely associated with active fluid flow within the active vema transform at crustal ages of ca 10 ma we found clear indications of fluid flow both in the sediments and the overlying water column this region is 120 km from the nearest spreading axis and increases by almost an order of magnitude the maximum off axis distance that active hydrothermal discharge has been found on the oceanic crust sampling of the igneous seafloor was possible at all crustal ages and the accretionary fabric imprinted on the plate during its production was prominent everywhere seafloor sediments show signs of extensive bioturbation in one area high concentrations of spherical mn nodules were also found and sampled at the end of the transect we also mapped and sampled the puerto rico trough a 8000 m deep basin north of the caribbean arc here the seafloor morphology is more complicated and strongly influenced by transpressive tectonics

ocean currents at axial volcano a northeastern pacific seamount 1 axial volcano is a magmatically active seamount that straddles the juan de fuca ridge jdfr with a summit depth of 1400 m the volcano intercepts deep ocean flows at a height well above that of the linear ridge adjoining it to the north and south multiyear yearlong observations of currents at axial show that mean flow circles the seamount in an anticyclonic sense consistent with dynamical constraints with means as large as 6 6 cm s 1 spectra of currents indicate prominent tidal inertial and in some cases weather band period 3 to 7 day peaks as has been seen elsewhere along the jdfr ridge for k1 o1 and s2 tidal currents at the seamount amplitudes are several times larger than the corresponding background amplitudes and rotation around the tidal current ellipses is anticyclonic m2 tidal currents show none of the same properties energy at the inertial frequency decreases by more than an order of magnitude from 100 m above to 400 m below the volcano s summit in contrast weather band wb period energy increases tenfold over the same depth range with wb energy all but unobservable at summit depth the presence of wb oscillations makes axial unlike other seamounts where long observations have been made the current meter observations also provide a picture of seasonal trends as expected during the period summer 1996 to spring 1997 largest amounts of wb energy are found during autumn and winter in contrast wb motion at axial volcano during winter 2000 was summer like in intensity a linear baroclinic model of forced damped azimuthal mode one oscillatory flow around an idealized axisymmetric seamount shows that amplification of diurnal flow should occur principally at the seamount summit while amplification of the wb should occur as the observations show on the seamount flanks model and measured phase relationships for temperature and current time series pairs circumscribing axial support the view that azimuthal mode one oscillations are prominent over the 0 8 to 6 day range for forcing period tc the model indicates that the principal topographic resonance as indicated by kinetic energy ke amplification occurs for a tc greater than 1 and less than 2 days with only mild dependence in that range on background stratification and seamount shape additional but weaker topographic resonances can occur at longer periods in model results but as tc becomes slightly larger than the frictional timescale topographic resonances no longer appear high dissipation and thus short frictional timescales reported by others in regions of rough sloping topography make topographic resonances at axial at periods greater than a few days somewhat unlikely the relatively broad wb spectral peaks at some axial sites are consequently more likely the result of spectral peaks in forcing than of topographic resonance

orbitally forced sedimentary rhythms in the stratigraphic record is there room for tidal forcing the imprint of orbital cycles which result from the varying eccentricity of the earth s orbit and changes in the orientation of its axis have been recognised throughout the phanerozoic rock record variations in insolation and their effect on climate are generally considered to be the sole transfer mechanism between the orbital variables and cyclic sedimentary successions common oceanographic principles however show that the ocean tide also responds to variations in the orbital parameters the ocean tide has not yet been considered to be a valid additional transfer mechanism for the orbital variations in geological studies of milankovitch cycles in sedimentary successions the insolation paradigm offers satisfying explanations and the role of long term variations of the ocean tide has not yet been appreciated variations in the ocean tide related to changing eccentricity at present 0 0165 theoretical maximum 0 0728 affect a variety of oceanographic and sedimentary processes in addition to the widely accepted paradigm of orbitally forced insolation changes the tidal transfer of orbital signals may explain certain less well understood aspects of orbitally induced cycles in the stratigraphic record related to ocean mixing organic productivity and tidal processes in shallow seas and deep water variations of the ocean tide in relation to the 18 6 year lunar nodal cycle which has no insolation counterpart by which they may be obscured indeed show that these relatively small variations can produce significant effects in sedimentary environments that are sensitive to variations in the strength of the ocean tide in analogy with the 18 6 year lunar nodal cycle orbital variations of the tide on milankovitch time scales are likely to have affected sedimentary systems in the past

dynamics of cloud features on uranus abstract near infrared adaptive optics imaging of uranus by the keck 2 telescope during 2003 and 2004 has revealed numerous discrete cloud features 70 of which were used to extend the zonal wind profile of uranus up to 60 n we confirmed the presence of a north south asymmetry in the circulation karkoschka e 1998 science 280 570 572 and improved its characterization we found no clear indication of long term change in wind speed between 1986 and 2004 although results of hammel et al hammel h b rages k lockwood g w karkoschka e de pater i 2001 icarus 153 229 235 based on 2001 hst and keck observations average 10 m s less westward than earlier and later results and 2003 observations by hammel et al hammel h b de pater i gibbard s lockwood g w rages k 2005 icarus 175 534 545 show increased wind speeds near 45 n which we do not see in our 2003 2004 observations we observed a wide range of lifetimes for discrete cloud features some features evolve within 1 h many have persisted at least one month and one feature near 34 s termed s34 seems to have persisted for nearly two decades a conclusion derived with the help of voyager 2 and hst observations s34 oscillates in latitude between 32 s and 36 5 s with a period of 1000 days which may be a result of a non barotropic rossby wave it also varied its longitudinal drift rate between 20 day and 31 day in approximate accord with the latitudinal gradient in the zonal wind profile exhibiting behavior similar to that of the ds2 feature observed on neptune sromovsky l a limaye s s fry p m 1993 icarus 105 110 141 s34 also exhibits a superimposed rapid oscillation with an amplitude of 0 57 in latitude and period of 0 7 days which is approximately consistent with an inertial oscillation

record breaking storm activity on uranus in 2014 abstract in spite of an expected decline in convective activity following the 2007 equinox of uranus eight sizable storms were detected on the planet with the near infrared camera nirc2 coupled to the adaptive optics system on the 10 m w m keck telescope on ut 5 and 6 august 2014 all storms were on uranus northern hemisphere including the brightest storm ever seen in this planet at 2 2 m reflecting 30 as much light as the rest of the planet at this wavelength the storm was at a planetocentric latitude of 15 n and reached altitudes of 330 mbar well above the regular uppermost cloud layer methane ice in the atmosphere a cloud feature at a latitude of 32 n that was deeper in the atmosphere near 2 bar was later seen by amateur astronomers we also present images returned from our hst too program that shows both of these cloud features we further report the first detection of a long awaited haze over the north polar region

tidal mixing processes amid small scale deep ocean topography the nature of tide topography interaction reflects the topographic scales experienced by water parcels during their tidal excursions in the deep ocean these scales are typically subkilometer yet direct observations of tidal processes on such scales are lacking at one site a saddle amid steep and complex mid atlantic ridge topography observations reveal tidally pulsed bottom trapped fronts overflows and lee waves in response to a tide combined with a mean flow of similar amplitude the tidal pulsing of the fronts and overflows was only evident locally and their phase became unpredictable over scales of hundreds of meters enhanced turbulence in a 100 200 m thick bottom boundary layer had an estimated dissipation rate of 2 6 10 2 w m 2 exceeding the large scale average of tidal dissipation in mid ocean ridge environments but by less than an order of magnitude this site was not a dissipation hotspot and the processes observed could provide widely distributed mixing to the meridional overturning circulation

actinium 227 as a deep sea tracer sources distribution and applications abstractactinium is one of the rarest naturally occurring elements on earth we measured its longest lived isotope 227ac half life 21 77 years for the first time in the water column of the southeast pacific the central arctic the antarctic circumpolar current acc and the weddell gyre besides the profile in the southeast pacific which confirms earlier findings about the role of diapycnal mixing for 227ac distribution we found three other different types of vertical profiles these profiles point to a prominent role of advection for 227ac distribution especially in the southern ocean depending on the type of profile found 227ac is proposed as a tracer for different oceanographic questions in the southern ocean up to 4 93 0 32 dpm m 3 227acex 227ac in excess of its progenitor 231pa are found close to the sea floor which are the highest concentrations ever observed in the ocean close to the sea surface in the weddell gyre wg 0 46 0 05 dpm m 3 227acex are detected we use 227acex there to determine the upwelling velocity in the eastern weddell gyre to be about 55 m y 1 in the acc upper and lower circumpolar deep water ucdw and lcdw are found to differ clearly in their 227acex activity high 227acex activities are therefore a promising tracer for recent inputs of lcdw to the sea surface which may help to understand the role of deep upwelling for iron inputs into antarctic surface waters the expected release of 227ac is compared with 228ra to make sure that the large near surface excess in the water column of the southern ocean is not due to lateral inputs by isopycnal mixing results of a model indicate that the 227ac 228ra flux ratio is about 50 times lower on shelves than in the deep sea data from the central arctic and from a transect across the acc confirm that 228ra and 227acex differ strongly in their sources the first measurements of 227ac on suspended matter less than 1 7 of total 227ac close to the sea floor indicate that the particle reactivity of 227ac is negligible in the open ocean in agreement with earlier findings nozaki 1984 despite the extremely low concentrations of 227ac new measurement techniques moore and arnold 1996 point to a comfortable and comparably simple determination of 227ac in the future finally 227acex may become a widely used deep sea specific tracer

dispersion of a tracer in the deep gulf of mexico a 25 km streak of cf3sf5 was released on an isopycnal surface approximately 1100 m deep and 150 m above the bottom along the continental slope of the northern gulf of mexico to study stirring and mixing of a passive tracer the location and depth of the release were near those of the deep hydrocarbon plume resulting from the 2010 deepwater horizon oil well rupture the tracer was sampled between 5 and 12 days after release and again 4 and 12 months after release the tracer moved along the slope at first but gradually moved into the interior of the gulf diapycnal spreading of the patch during the first 4 months was much faster than it was between 4 and 12 months indicating that mixing was greatly enhanced over the slope the rate of lateral homogenization of the tracer was much greater than observed in similar experiments in the open ocean again possibly enhanced near the slope maximum concentrations found in the surveys had fallen by factors of 104 107 and 108 at 1 week 4 months and 12 months respectively compared with those estimated for the initial tracer streak a regional ocean model was used to simulate the tracer field and help interpret its dispersion and temporal evolution model data comparisons show that the model simulation was able to replicate statistics of the observed tracer distribution that would be important in assessing the impact of oil releases in the middepth gulf