bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion of sea ice
Authors: Thorndike A. S.
Published: February 2008

The field of motion of sea ice is such that a Lagrangian element will be progressively deformed. The deformation can be resolved into a smooth part analogous to the distortion of a highly viscous fluid plus a random and discontinuous part having some similarity to the random motion of a turbulent fluid and the discontinuous motions of plate tectonics. The Lagrangian element spreads out at a rate determined by the mean field and by the random field, but the mean field usually is more important. The importance of the random field is that it gradually mixes the Lagrangian element with the surrounding ice. A mechanism for this mixing is discussed. The simplest mode of deformation for sea ice may be a finite shear displacement along a single crack. If the ice deforms in this way, first along one crack, then along another, and eventually along a sequence of randomly oriented cracks, the result will be a complete reshuffling of the ice pack. Nearby points disperse. Compact regions become fragmented. This model can be tested against observations of ice motion. In terms of the relative diffusion of pairs of points, the model predictions have a weak resemblance to actual ice behavior.
Low‐frequency circulation on the Texas‐Louisiana continental shelf
Authors: Cochrane J. D. , Kelly F. J.
Published: February 2008

For the Texas‐Louisiana coast west of 92.5°W, long series of data from near Freeport, Texas, together with shorter series from other locations, show strong response of coastal current to wind stress in agreement with coastal jet concepts. We infer from coastal winds, scattered current measurements, and distributions of sea‐surface salinity and geopotential that a cyclonic gyre elongated along the shelf is the dominant feature of the prevailing shelf circulation. The inshore limb of the gyre is the coastal jet driven by wind with a west or southward (downcoast) component which prevails along much of the coast except in July‐August. Because the coast is concave, the shoreward prevailing wind results in a convergence of coastal currents, which marks the downcoast extent of the gyre. Corresponding to the convergence is a seaward flow which forms the southwest limb of the gyre. A prevailing countercurrent (north or eastward flow) along the shelf break includes the outer limb of the gyre. The eastern, shoreward‐flowing limb of the gyre corresponds to divergence along the coast centered near 92.5°W. The convergence at the western or southern end of the gyre migrates seasonally with the direction of the prevailing wind, reaching south of the Rio Grande mouth in fall and the Cameron offing in July. The gyre is normally absent in July, but reappears in August‐September when a downcoast wind component develops.
Return periods of extreme sea levels from short records
Authors: Middleton John F. , Thompson Keith R.
Published: February 2008

Extreme sea levels usually arise from a combination of the tides (assumed here to be deterministic) and storm surges (assumed stochastic). We show in this paper how tide and surge statistics derived from short (∼1 year) records can be used to predict the occurrence of extremes with much longer return periods (∼50 years). The method is based on an extension of the exceedance theory originally developed by Rice (1954) to study noise in electrical circuits. A comparison of predicted return periods with those obtained directly from a 50‐year Markovian simulation of surge is used to validate the exceedance probability method. The method is next applied to the Canadian ports of Halifax and Victoria, which are dominated by semidiurnal and diurnal tides, respectively. To provide a stringent test of the method, just 1 year's data from each port are used to estimate the tide, surge statistics, and hence return periods. The predictions are found to compare well with the results of a conventional (Gumbel) extremal analysis based on more than 60 years of data provided allowance is made for (1) the anormality of the surge distribution and (2) seasonal changes of surge variance. The agreement suggests that the method may be successfully applied to other short sea level records or indeed to any partly deterministic process where return periods are of interest.
Empirical orthogonal function analyses of tropical Atlantic sea surface temperature and wind stress: 1964–1979
Authors: Servain Jacques , Legler David M.
Published: February 2008

Scalar and vector empirical orthogonal function (EOF) analyses have been performed on monthly sea surface temperature (SST) and wind stress within the tropical Atlantic region for the years 1964–1979. The long‐term average was subtracted from the 16‐year SST and wind stress monthly fields to focus on the seasonal variability and its interannual modulations. A smaller cumulative percent of variance accounted for by the first eigenvectors of wind stress reflects the greater variability of the wind than that of SST. Analysis of regional seasonal SST events requires a combination of the first three EOFs, whereas the dominant events of the seasonal cycle of the wind stress are adequately represented by E1 and E2. As in the Pacific, an increase of the trade wind system is observed between the 1960s and the 1970s. Our analyses provide diagnostic insight into two types of large spacetime scale episodes. The first type is exemplified by the following sets of observations: during the spring of 1968 (spring 1976), an abnormal relaxation (intensification) of the wind stress occurred in both the northeasterlies and the southeasterlies. Subsequently, equatorially trapped anomalous warming (cooling) occurred inside the Gulf of Guinea. The second type is exemplified by the following: during 1972 to 1975, the northeasterlies (stronger) and the southeasterlies (weaker) acted out of phase, leading to a more global response of the ocean. The oceanic response was different in the northern (colder) and southern (warmer) basins.
Tidal currents seaward of the Northern California Continental Shelf
Authors: Noble Marlene , Rosenfeld Leslie K. , Smith Robert L. , Gardner James V. , Beardsley Robert C.
Published: February 2008

Current measurements obtained from a sparse array of moorings deployed over the slope and the adjacent deep‐sea basin off northern California for 4 to 14 months have been analyzed for their tidal constituents. The M2 tidal currents were the strongest tidal constituent, containing 50% to 75% of the total current variance in the four major tidal bands. The semimajor axis of the M2 constituent ranged from 2 to 4 cm s−1 and tended to be aligned with the local topography. Internal tides, which were usually present in the M2 band, were often the dominant cross‐slope current component on the middle slope. At least a portion of the internal tidal current field had a steady phase that slowly changed over 1 to 2 months. The semimajor axes of the diurnal barotropic ellipses had amplitudes ranging from 0.7 to 1.2 cm s−1 and were oriented both parallel and perpendicular to the local topography. These tidal current measurements suggest that the barotropic diurnal currents propagate poleward as a combination of Kelvin and continental shelf waves and that the barotropic M2 tides propagate poleward primarily as a Kelvinlike wave. Battisti and Clarke's (1982) model, which uses coastal sea level data to predict M2 tidal currents, agrees reasonably well with the observations presented here, indicating that the model can be used to predict the M2 currents seaward of the middle slope off Northern California.
Renewal rates of East Atlantic deep water estimated by inversion of 14C data
Authors: Schlitzer Reiner
Published: February 2008

The renewal of the deep water of the East Atlantic and its large‐scale internal circulation are studied on the basis of the distributions of potential temperature, silicate, ΣCO2, and 14C. An isopycnal multibox model including advection, mixing, and sources and sinks is set up and described. Tracer data are input for the model, and balance equations for the various properties for the boxes of the model serve as constraints for the determination of water fluxes, mixing coefficients, and source parameters. Extremal values for various model parameters that are consistent with the tracer data (satisfy the balance equations within the estimated tolerances) are calculated by linear programming techniques. 14C data are seen to be valuable in determining absolute flow rates. Model results confirm the importance of the Romanche Facture Zone for the renewal of east Atlantic deep water. Eastward flows through the Romanche Fracture Zone were found to be between 2.6 and 5.1 Sv. Flows through the Vema Fracture Zone amount to at most 20% of the Romanche Fracture Zone inflow. Contributions of Antarctic Bottom Water at the southern end of the East Atlantic (Walvis Ridge) and of Iceland Scotland Overflow Water at the northern end are very small (< 5% of equatorial inflow). Diapycnal mixing coefficients are between 1 and 10 cm2/s, and values for the dissolution rates of silicate and carbon are in the expected range.
Reynolds stresses under wind waves
Authors: Cavaleri Luigi , Zecchetto Stefano
Published: February 2008

This paper describes a series of wave measurements, taken from an oceanographic tower, concerning water particle kinematics. Attention is focused on the phase relationship between surface elevation and the velocity components. Large phase shifts with respect to the expected values are found under active wave conditions, while swell behavior closely follows the linear theory. The reliability of the measurements is analyzed in detail. Possible physical reasons for the findings are indicated in the final discussion.
Seasonal oxygen cycles and biological new production in surface waters of the subarctic Pacific Ocean
Authors: Emerson Steven
Published: February 2008

Seasonal cycles of oxygen, temperature and salinity at Ocean Weather Station P in the subarctic Pacific Ocean reveal a regular 4–6% supersaturation of oxygen in the surface waters during the summers of the 10‐year period 1969–1978. The main processes causing super‐saturation are surface water heating and the net effect of primary production and community respiration. The biological and heating signals are separated using a mixed layer model and estimates for the air‐water gas exchange rate calculated from empirical correlations to wind speed. Biological new production during the summer (mid‐May to mid‐August) is estimated to be 100–300 mg C m−2 d−1. These values are within the range of independent estimates calculated from the summer nitrate depletion. There is a factor of 3 variation in the new production estimates during the period 1969–1978 with a minimum in 1973–1975. This trend is positively correlated with the interannual variation in zooplankton standing stock at station P.
Eddy near the Molloy Deep revisited
Authors: Bourke Robert H. , Tunnicliffe Mark D. , Newton John L. , Paquette Robert G. , Manley T. O.
Published: February 2008

A warm, 60‐km‐diameter cyclonic eddy was observed in late summer 1984 in the vicinity of the Molloy Deep at the eastern edge of the East Greenland Current. Depression of isotherms to at least 900 m indicates a deep‐reaching baroclinicity. Maximum baroclinic speeds of 0.1 to 0.17 m/s are estimated, as is a swirl transport of 1 Sv.
The role of shortwave radiation in the summer decay of a sea ice cover
Authors: Maykut Gary A. , Perovich Donald K.
Published: February 2008

Heat balance models of ice, leads, and the underlying water column were used to investigate the role of shortwave radiation in the summer decay of a sea ice cover. Because of the potential importance of positive feedback between decreasing ice concentration and increasing solar input to the ocean, particular emphasis was given to the treatment of heat transfer and lateral melting in leads. The rate of heat loss to floe edges was calculated from lead temperatures using an empirical boundary layer parameterization. Coefficients for this parameterization were obtained from field measurements in the dynamically active ice cover of the Greenland Sea during the 1984 Marginal Ice Zone Experiment and in the static ice of Mould Bay, Northwest Territories. Field coefficients were found to be considerably larger than those previously obtained in the laboratory, suggesting that heat transfer rates near floe edges were controlled more by winds and currents than by local density differences. Model studies of individual leads indicate that heat losses to the atmosphere cause lateral melt rates to asymptotically approach a constant value as lead size increases. Thus although very wide leads transmit considerable energy to the underlying ocean, they have relatively little effect on lateral melting. Other results provide information on the relative importance of horizontal heat transfer rates, ice thickness, floe perimeter, atmospheric forcing, and oceanic heat flux. In general, the calculations indicate that much of the shortwave radiation entering the ocean is absorbed below the ice where it contributes to bottom ablation rather than lateral melting. This suggests that previous work has seriously overestimated the magnitude of the feedback between ice concentration and incident shortwave radiation.
A new numerical method for surface hydrodynamics
Authors: West Bruce J. , Brueckner Keith A. , Janda Ralph S. , Milder D. Michael , Milton Robert L.
Published: February 2008

We present a new numerical method for studying the evolution of free and bound waves on the nonlinear ocean surface. The technique, based on a representation due to Watson and West (1975), uses a slope expansion of the velocity potential at the free surface and not an expansion about a reference surface. The numerical scheme is applied to a number of wave and wave train configurations including longwave‐shortwave interactions and the three‐dimensional instability of waves with finite slope. The results are consistent with those obtained in other studies. One strength of the technique is that it can be applied to a variety of wave train and spectral configurations without modifying the code.
Indonesian through flow and the associated pressure gradient
Authors: Wyrtki Klaus
Published: February 2008

The flow of water from the western Pacific to the eastern Indian Ocean through the Indonesian archipelago is governed by a strong pressure gradient. Dynamic height computations determine the average sea level difference as 16 cm and show that most of the pressure gradient is contained in the upper 200 m. Sea level data from Davao in the Philippines and from Darwin in Australia are used to determine the annual signal and the interannual variations of the pressure gradient for the years 1966 to 1985. The annual signal has a maximum during the southeast monsoon in July and August and a minimum in January and February. Interannual variations are not related to the Southern Oscillation because sea level is low at both stations during El Niño events, and thus there is little influence on the sea level difference. The mechanism of the through flow is discussed, but a determination of its numerical value will have to await direct measurements. A comparison of the sea level difference with results from a numerical model by Kindle shows satisfactory agreement. It is concluded that the variability of the through flow can be monitored by sea level measurements.
Coastal upwelling and eddy development off Nova Scotia
Authors: Petrie Brian , Topliss Brenda J. , Wright Daniel G.
Published: February 2008

Satellite photos during the summer of 1984 show the development of a band of cool water along the seaward coast of Nova Scotia during a month‐long period of upwelling favorable winds. The timing of the appearance of the cool water band, the rate at which it broadened, and the bottom‐temperature evolution at several representative points along the coast are shown to be in good agreement with an idealized two‐layer model of the wind‐driven shelf circulation. The presence of the cool water is clearly attributable to upwelling. After the temperature front moves offshore, wavelike features develop rapidly with alongshore wavelengths of 50–75 km and similar maximum cross‐shore displacement amplitudes. The associated alongshore propagation speed is at most 0.02 m s−1 to the northeast. The length and time scales of these features are shown to be consistent with results from simple linear instability models which allow for both potential and kinetic energy release from the mean state by perturbations. Results suggest that the wavelike features are primarily due to baroclinic instability of the upwelling‐associated base state. Rough estimates suggest that upwelling and subsequent eddy development can play an important role in the supply of nutrients to the surface waters of the shelf.
Coastal upwelling off Peru during normal and El Niño times, 1981–1984
Authors: Huyer Adriana , Smith Robert L. , Paluszkiewicz Theresa
Published: February 2008

Repeated conductivity, temperature, and depth (CTD) sections were made across the continental margin off Peru at 5°S and 10°S between November 1981 and May 1984, i.e., before, during, and after El Niño of 1982–1983. Coastal sea level at Paita (5°S) and Callao (12°S) began to rise in early October 1982 and returned to normal in July 1983. Coastal winds, which are normally favorable for upwelling, remained normal during October 1982; between November 1982 and May 1983 they were weaker than normal at Talara and Paita (5°S) but stronger than normal at Callao (12°S). Between mid‐March and mid‐April 1983, winds at 5°S were very weak or even unfavorable for upwelling. Repeated CTD sections at 5°S show signs of active upwelling (a negative onshore surface temperature gradient and upward sloping isotherms near the coast) whenever local winds were favorable for upwelling, but not when winds were calm or unfavorable. At 10°S, winds remained favorable for upwelling throughout El Niño. At both 5°S and 10°S, the apparent source depth of upwelling waters, 50–100 m, remained the same before, during, and after El Niño; this layer is normally below the thermocline, but during El Niño it was at the top of the depressed thermocline. The upwelling that occurred during El Niño resulted only in the upwelling of warm, nutrient‐poor waters. In May 1983, a CTD section at 10°S indicated that upwelling had ceased there in spite of continued strong, upwelling‐favorable winds; this cessation of upwelling is attributed to an alongshore pressure gradient that persisted from mid‐March to mid‐June 1983, causing onshore geostrophic flow to balance the wind‐driven offshore flow in the surface layer.
Effects of the 1982–1983 El Niño on the marine phytoplankton off northern Chile
Authors: Avaria Sergio , Muñoz Pablo
Published: February 2008

The evolution of phytoplankton was studied between December 1980 and August 1985. A total of 1269 net and water samples were obtained in 11 cruises as part of the Estudio Regional del Fenómeno El Niño‐Chile Program covering the area extending from Arica (18°30′S) to Chañaral (26°20′S) from the coast to 200 n. mi (370 km) westward. In the period which preceded the 1982–1983 El Niño event, the coastal phytoplankton consisted predominantly of blooming diatom species which support a large phytoplanktonic biomass. The cell density up to 20 n. mi (37 km) off the coast was over 100 cells mL−1, with a maximum density nucleus near the coast, where values over 1000 cells mL−1 were found. With the anomalous conditions produced by El Niño in December 1982, changes were detected in the phytoplankton biomass and composition. There was a marked decrease in the biomass, the diatom dominance was restricted to a narrow coast band of 2 to 3 n. mi (3.7–5.5 km), and warm water species of diatoms and dinoflagellates reached the coast. These conditions reached their maximum intensity in May 1983. Phytoplankton started to return to normal conditions in December 1983 with a predominance of large diatoms, which support a biomass somewhat larger than that during El Niño. Small diatoms returned as the dominant species in large blooms in 1985. The cell numbers reached values similar to those during pre‐Niño conditions, with a normal neritic and oceanic phytoplankton distribution. Red tides caused by the ciliate Mesodinium rubrum were common during normal conditions before and after El Niño.
A review of geological evidence for ancient El Niño activity in Peru
Authors: DeVries Thomas J.
Published: February 2008

Geological evidence (geomorphological, sedimentological, paleontological, and archeological) for the occurrence of El Niño events in Peru during the Quaternary has been reevaluated. New data concerning thermally anomalous molluscan assemblages in Holocene deposits of north central Peru are briefly described, as are new data regarding the distribution of warm‐ and cold‐ water mollusks in late Pliocene and early Pleistocene deposits of northwestern Peru. No conclusive evidence of prehistoric “El Niño” events was found in the new data or the reviewed literature. Most references to El Niño events are best characterized as descriptions of El Niño‐ like conditions. These conditions may accurately represent events or only mimic events. Past studies lack evidence of two necessary criteria for proof of an El Niño event: a demonstrably short‐lived event, and the advection of warm coastal marine waters into the southeastern Pacific Ocean. The glaciological record of precipitation in the Andes, when combined with historical accounts of El Niño phenomena on the coast, is the sole example of a geological data set that meets both criteria.
Diurnal response of sea surface temperature observed at the long‐term upper ocean study (34°N, 70°W) in the Sargasso Sea
Authors: Price James F. , Weller Robert A. , Bowers Clarke M. , Briscoe Melbourne G.
Published: February 2008

Air‐sea observations made by the Long‐Term Upper Ocean Study in the Sargasso Sea are used to determine how the diurnal response of sea surface temperature ΔTs depends upon surface heating H and wind stress S. The data set analyzed here is extensive, spanning two full summers and 361 days in total. It samples virtually the full range of possible heating conditions, and ΔTs varies from zero up to 3° C. There is a clear trend of increasing ΔTs with increasing H or decreasing S (the qualitative result expected). A smooth function calculated as an average from the data itself can account for about 90% of the variance of ΔTs, showing a direct and significant dependence of ΔTs upon H and S. The analyzed data are compared to a theoretical model developed under the assumption that wind stress causes vertical mixing via shear flow instability. This model can account for about 80% of the observed variance and shows an H, S dependence consistent with the data.
The ice thickness distribution across the Atlantic sector of the Antarctic Ocean in midwinter
Authors: Wadhams Peter , Lange Manfred A. , Ackley Stephen F.
Published: February 2008

During the first leg of the Winter Weddell Sea Project (Antarktis V/2) cruise of F.S. Polarstern the entire width of the Antarctic sea ice zone was traversed in the vicinity of 0° longitude in the period July 18 to September 10, 1986. Ice thicknesses were measured by direct drilling and by helicopter profiling using an Exstar 100‐MHz impulse radar system. In addition, aerial photography of the ice cover was done from 100‐ to 2000‐m altitude using a 70‐mm aerial camera mounted in the helicopter. The results of the point measurements (drilling) are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area‐averaged ice thickness distributions. It was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes; this formed out of a 250‐km‐wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice. Preferred thicknesses of undeformed floes were 40–60 cm of ice covered with 5–15 cm of snow. The individual pancakes attained almost all of this thickness before consolidation; subsequent congelation growth was slow, estimated at 0.4 cm d−1. The floes contained much small‐scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation, but pressure ridging was modest except in the far south. A few very thick (8–11 m) multiyear floes were observed embedded in the pack at latitudes beyond 66° S.
Microbubbles: Stabilization by monolayers of adsorbed particles
Authors: Johnson Bruce D. , Wangersky Peter J.
Published: February 2008

Stable microbubbles are a ubiquitous feature of natural waters, acting as sites for mechanical and acoustical cavitation and nucleii for bubble growth at low gas super‐saturations. Stable microbubble populations that have been determined acoustically in the past are not well explained by existing models of bubble stabilization, i.e., stabilization in particle crevices or stabilization by molecular monolayers. Based upon the observation that bubbles rising in sea water rapidly become coated with particles, a model is developed in which bubbles are stabilized mechanically by monolayers of adsorbed nonpolar particles. Long‐term bubble stability is demonstrated in laboratory experiments. Predictions based on the experiments and the model are, in order of magnitude, consistent with observation.
On the parameterization of irradiance for open ocean photoprocesses
Authors: Siegel David A. , Dickey T. D.
Published: February 2008

Measurements of downwelling spectral irradiance were made during the fall of 1982 in the North Pacific Ocean (near 33°N, 142°W). These data are used to produce vertical profiles of downwelling irradiance for visible energy (400–700 nm) and photosynthetic available radiation (PAR). The profiles demonstrate that the attenuation of visible energy and PAR are primarily functions of chlorophyll pigment concentration and depth. Commonly used parameterization methods for radiant fluxes and their attenuation, which are based upon either optical water type or mean chlorophyll pigment concentration, do not yield results which compare favorably with the observed profiles. A new parameterization method for the estimation of open ocean in situ radiant fluxes is presented. This method assumes that chlorophyll pigments and pure seawater control the attenuation of spectral irradiance and that the downwelling radiant fluxes just beneath the sea surface are directly proportional to the incident solar flux. Results obtained with this method are in good agreement with the observations. The use of pigment concentrations to characterize attenuation eliminates the need to rely upon empirical optical water mass types, which do not account for temporal or spatial variations of attenuating materials. The present parameterization enables a direct optical coupling between physical and biological processes and is applicable to open ocean observational and modeling studies.
A numerical model of the combined wave and current bottom boundary layer
Authors: Davies A. G. , Soulsby R. L. , King H. L.
Published: February 2008

A numerical model of oscillatory rough‐turbulent boundary layer flow, featuring closure via the turbulent energy equation, is used to examine the principal features of wave‐current interaction above the seabed. Results are presented from case studies carried out with water depth of 10 m, bed roughness of 0.5 cm and wave period of 8 s. The steady surface current in the absence of waves is nominally 100 cm/s, and waves having near‐bottom velocity amplitudes of 50, 100, and 150 cm/s are superimposed on this current at angles ϕ = 0, π/4, and π/2. Velocity, turbulent energy, shear stress, and eddy viscosity distributions are compared for the steady current alone, for waves alone, and for waves superimposed on the current, and the interaction in the wave‐current boundary layer is examined. Cycle‐averaged vertical profiles of horizontal velocity illustrate the extent to which the mean flow is retarded by wave‐current interaction. For the general case in which the waves are superimposed at an arbitrary angle ϕ, the mean current veers to form an angle with the wave direction greater than that of the initial steady current. Finally, the enhancement of the bed shear stress and the increase in oscillatory boundary layer thickness associated with wave‐current interaction are both quantified.
The available potential energy of an isolated feature
Authors: Hebert Dave
Published: February 2008

The true available potential energy (APE) of an isolated feature (e.g. a warm‐core ring) in a basin is the difference in the potential plus internal energy between the observed and reference state. The reference state is that in which the same fluid is redistributed adiabatically to a stably stratified state and the isopycnals are on constant geopotential surfaces. For an isolated feature in an infinitely wide basin, it would seem reasonable to assume that the far‐field density structure is a good approximation of the reference state. This approximation to the reference state will be examined in this paper. Four different methods of calculating the available potential of an isolated feature are compared. These are (1) the gravitational available potential energy using the reference state (APEG), (2) the gravitational available potential energy using the far‐field density structure as an approximation for the reference state, (3) the Boussinesq available potential energy using the reference state (APEB), and (4) the Boussinesq available potential energy using the farfield density structure instead of the reference state. The gravitational available potential energy using the reference state (APEG) is the true available potential energy for an incompressible fluid. Therefore the different approximations of the available potential energy can be compared to the APEG of an isolated feature in an infinitely wide basin. It is found that the gravitational available potential energy using the far‐field density structure has an offset which depends on the density structure of both the feature and far field. Therefore the APEG using the far‐field density structure is not a good method for calculating the APEG of an isolated feature in an infinitely wide basin, and the reference state must be calculated. We examine the limitations on the Boussinesq approximation for the APE. It is found that the isopycnal displacement from its reference state must be smaller than a length scale based on the reference state buoyancy frequency
. Also, the maximum separation of isopycnals in the observed state must be less than twice the average separation of the isopycnals. With these conditions satisfied, the APEB approximates the APEG of an isolated feature. The Boussinesq APE using the far‐field density structure instead of the reference state gives the asymptotic limit of the APEG of an isolated feature in an infinitely wide basin. A simple stratified model of an isolated feature is used to demonstrate the difference between these different available potential energy estimates. Finally, the APE estimates using some data from a survey of a Mediterranean salt lens are compared.
Spray droplet generation, transport, and evaporation in a wind wave tunnel during the humidity exchange over the sea experiments in the simulation tunnel
Authors: Mestayer Patrice , Lefauconnier Claude
Published: February 2008

The HEXOS Experiments In the Simulation Tunnel (HEXIST) are part of the continuing Humidity Exchange Over the Sea program (HEXOS). It is actually an international cooperative subprogram focused on the local interactions between spray droplets and the turbulent fields of velocity, temperature, and humidity. It incorporates numerical modelling and wind tunnel experiments. In order to study separately the generation of droplets, their transport and diffusion by turbulence, their evaporation, and their deposition, a new experimental approach has been designed, based on the generation of spray droplets by the bursting of bubbles produced by aeration devices immersed in the water tank of the large air‐sea interaction simulation tunnel at the Institut de Mécanique Statistique de la Turbulence, Marseille, France. This paper presents this approach, the experimental setup, the governing equations, and the results of the feasibility experiments.
Gulf Stream velocity structure through inversion of hydrographic and acoustic Doppler data
Authors: Pierce Stephen D. , Joyce Terrence M.
Published: February 2008

Near‐surface velocities from a shipborne acoustic Doppler instrument are used together with conductivity‐temperature‐depth and O2 data to make estimates of geostrophic velocities off of Cape Hatteras. The data set consists of two transects across the Gulf Stream at approximately 73°W and 71°W made by the R/V Endeavor in August 1982. An inversion technique is applied which makes use of both the acoustic Doppler data and property conservation requirements. The method produces estimates of the absolute flow field across the two sections with formal errors of 1–2 cm/s. At the time of the observations, the net Gulf Stream transports are estimated to be 116±2×109 kg/s at 73°W and 161±4×109 kg/s at 71°W. A southwestward Deep Western Boundary Current transport is estimated at 4±1×109 kg/s. Taken together with recent Gulf Stream transport estimates of similar accuracy made in June 1982, the results are in general larger than historical transport estimates in this region.
Ice breakup: Observations of the acoustic signal
Authors: Waddell S. R. , Farmer D. M.
Published: February 2008

We describe observations of ambient sound beneath landfast ice in the Canadian Arctic Archipelago and interpret its evolution over the period June–August in terms of ice cracking and disintegration. The data were recorded on six bands between 50 and 14,500 Hz for the period April 2 to August 7, 1986, in Dolphin and Union Strait. The frequency dependence of the attenuation of sound in water allows separation of distant and local noise sources. In conjunction with satellite imagery and meteorological data, it is shown that strong signals in the acoustic time series are associated with major breakup events. The acoustic signal can provide predictive information about ice conditions and the approach of breakup.
Response of a floating sea ice sheet to a steadily moving load
Authors: Takizawa Takatoshi
Published: February 2008

An extended analysis of previous experimental work (Takizawa, 1985) is made. Using the dispersion relation for flexural free waves in a floating ice sheet, a diagram that predicts the critical speed, at which the ice deflection is amplified markedly, is presented. An understanding of the group velocity provides one explanation for the question why two waves appear in front of and at the rear of the load. The two‐dimensional deflection patterns obtained in the experiment are compared with the existing theoretical results. At high speeds the ice beneath the load is found not to be depressed but somewhat elevated. It is shown that viscous damping has substantial effects on the ice deflection profile. The wave number curves, which give the two‐dimensional wave patterns, are also examined, and the results verify that a one‐dimensional model quite adequately describes the wave characteristics in Takizawa's experiment.
Shallow equatorial jets
Authors: Firing Eric
Published: February 2008

When zonal velocity profiles from the central equatorial Pacific are expanded into sums of vertical normal modes, the peak amplitudes occur consistently near modes 1, 5, 12, and 18. The first two of these peaks sum to a recognizable equatorial undercurrent profile. The two higher‐mode peaks blunt and thicken the equatorial undercurrent (EUC) and add a westward extremum near 340 m. During the 1982–1983 El Niño, the low‐mode component of the flow (modes 1–10) was more variable than the residual component, which was dominated by the modes near 12 and 18. The residuals below 120 m persisted as alternating westward and eastward current bands (the “shallow jets”) through the disappearance of the EUC in the second half of 1982 and its reappearance in 1983. The shallow jets were nearly constant in depth until late 1982 and then gradually rose through the end of the time series in June 1983. Differences in temporal behavior among the mode amplitude peaks indicate that these peaks are describing dynamically separate components of the flow which are not tightly coupled on time scales shorter than a few months.
Modeling ice dynamics of coastal seas
Authors: Overland James E. , Pease Carol H.
Published: February 2008

A coupled sea ice, barotropic ocean model with a 1‐km resolution and a seaward domain of 200 km quantifies three coastal processes: coupling of ice motion to wind‐driven coastal currents, ice thickness redistribution under compaction at the coast, and formation of coastal shear zones. The model consists of an ice momentum balance, mass concentration and two‐parameter ice thickness distribution, and equations for horizontal water motion and continuity using vertical structure functions. An appropriate constitutive law appears to be a hardening plastic based on qualitative observations from Alaskan continental shelves. For first‐year sea ice, strength is taken to be proportional to the square of ice thickness. A north wind example of 10 m/s with the coastline to the west shows the depth dependence of rotational shear in the sea ice/ocean boundary layer and sea surface tilt which contributes an alongshore slope current. There is slight convergence of sea ice over the shelf, a coastal shear zone of 4 km, and an alongshore ice speed seaward of the shear zone of 6% of the wind speed caused by the combination of an under‐ice shear layer and an alongshore slope current. For an onshore wind, ice is near free drift at 3% of the wind seaward of a ridging front, which propagates seaward. A square dependence of ice strength on thickness is required for the rubble field to approach a limiting thickness, consistent with observations. The hardening plastic interpretation of the rubble field has the stress state at the yield limit in contrast with a rigid plastic of high constant strength that yields only at the coast. We conclude that (1) ice thickness/motion feedback is important on scales less than 10 km, (2) the observational base to discriminate between mesoscale constitutive laws is not yet available, and (3) the relation of ice velocity to wind stress is variable because the ocean slope current responds only to the alongshore component of the wind.
Wave transformation and swash oscillation on gentle and steep slopes
Authors: Kobayashi Nobuhisa , DeSilva Gunamuni S. , Watson Keith D.
Published: February 2008

The numerical model developed previously for coastal structures is slightly modified and applied to predict the wave transformation in the surf and swash zones on gentle slopes as well as the wave reflection and swash oscillation on relatively steep beaches. The numerical model is one‐dimensional in the cross‐shore direction and is based on the finite amplitude, shallow water equations, including the effect of bottom friction, which are solved in the time domain for the incident wave train specified as input at the seaward boundary of the computation located outside the breakpoint. The slight modification is related to the effect of the time‐averaged current on the seaward boundary condition and improves the agreement between the computed and measured mean water levels on gentle slopes. The modified numerical model is compared with available small‐scale test data for monochromatic waves spilling on gentle slopes as well as for monochromatic waves plunging and surging on a relatively steep slope. Additional comparisons are made with small‐scale tests conducted using transient monochromatic and grouped waves on a 1:8 smooth slope with and without an idealized nearshore bar at the toe of the 1:8 slope. As a whole, the numerical model is shown to be capable of predicting both time‐varying and time‐averaged hydrodynamic quantities in the surf and swash zones on gentle as well as steep slopes.
Mean zonal currents below 1500 m near the equator, 159°W
Authors: Firing Eric
Published: February 2008

Recent current measurements have shown that the subthermocline equatorial circulation in the central Pacific is considerably more complicated than had been thought. Below 1500 m depth on 159°W there are three currents south of the equator that appear to be permanent. Eastward currents are found at 1700 m and 3100 m, and a westward current is found at 4000 m. The 1700‐m current is at the southern edge of the 3°S to 3°N range of current measurements, so its meridional extent and its transport are unknown. The 3100‐m and 4000‐m currents have 16‐month mean transports of about 6 − 7 × 106m3s−1. All three of these currents may be important components of the general circulation.
The decay of wind‐forced mixed layer inertial oscillations due to the β effect
Authors: D'Asaro Eric A.
Published: February 2008

Wind generation of mixed layer near‐inertial frequency oscillations has been observed and successfully modeled many times. Modeling of the decay of these currents by linear wave theory has been more difficult because the necessary horizontal scales are much smaller than the typical horizontal scales of the wind. A new, and highly effective, mechanism for generating such scales by the β effect is proposed here. An asymptotic analysis of the linear equations is presented which suppresses high‐frequency gravity waves and thus simplifies the near‐inertial frequency dynamics. The computed residence time for inertial motions in the mixed layer depends both on the scales of the wind and on β, with β imposing an upper limit of 1–2 weeks. The relative importance of the wind and β is estimated using realistic wind stress fields, generated by advecting Seasat scatterometer data over the simulated ocean. The predicted horizontal scales and decay times of mixed layer inertial motions are similar to those observed. The subsynoptic scales of the wind, the advection speed, and β are all important in determining the decay time of the simulated mixed layer inertial currents.
A theoretical study of diagenetic concentration fields near manganese nodules at the sediment‐water interface
Authors: Boudreau Bernard P. , Taylor Robert J.
Published: February 2008

The effects of manganese nodules on concentration fields in adjacent pore waters and sediments are investigated theoretically with a three‐dimensional (axisymmetric) diffusion‐reaction model. The nodules are idealized as impermeable and poorly permeable disks and hemispheres. The first part of this paper examines the organic matter and coupled pore water oxygen fields in order to evaluate the local redox conditions under an isolated nodule. Oxygen is allowed to disappear on a free surface that is calculated as an output of the model. In sediments that become suboxic, like those at MANOP site C, the model predicts that pore waters neighboring a nodule are markedly more depleted in oxygen than in its absence. Although these reduced conditions may remobilize metals that would be available for nodule growth, these same conditions would appear to favor nodule dissolution. Typically, the presence of a nodule raises the local position of the zero‐oxygen surface, but it is deeper than expected for large nodules on sediments containing only highly reactive organic matter. The redox changes calculated for an isolated nodule on a hypothetical, but representative, oxidized abyssal red clay appear inadequate to raise the redox boundaries enough to facilitate metal transport from reduced regions deeper in the sediment. In the later part of the paper the model is used to evaluate the influence of a nodule field on the outward flux of dissolved silica from a siliceous ooze. Although the flux attenuation is generally modest, some dense packings observed in the Pacific should produce substantial reductions (>35%), which should promote opal preservation.
Generation of internal waves by sea ice
Authors: McPhee Miles G. , Kantha Lakshmi H.
Published: February 2008

Observations in the Greenland Sea marginal ice zone suggest that when strong stratification occurs near the surface, momentum flux into the internal wave field of the upper ocean can be a major component of the force balance that governs ice drift. Since energy is radiated away by the internal waves, turbulent mixing and heat flux are also affected. We investigate the downward flux of momentum and energy by internal waves in an ice‐covered ocean, with an idealized model comprising a mixed layer overlying a deep, uniformly stratified layer. A buoyancy jump separates the mixed layer from the pycnocline. Drag from a single wave number component of the under‐ice roughness spectrum is derived as the product of a drag coefficient (based on ice speed, under‐ice roughness wave number and amplitude, and uniform stratification to the ice‐ocean interface) times an attenuation factor that depends additionally on mixed‐layer depth and the buoyancy jump at the base of the mixed layer. The model is extended to a plausible spectrum of under‐ice roughness by integration over wave number space. Internal wave effects are parameterized in terms of the drag coefficient from the integrated spectrum and incorporated into an upper ocean turbulence model. Model calculations show that plausible values for the peak wave number of the idealized spectrum and roughness variance can account for (1) decreased ice velocity relative to the wind, (2) decreased heat exchange coefficient between the ice and ocean, and (3) lack of mixed‐layer deepening, all of which were observed during the last week of the 1984 Marginal Ice Zone Experiment.
Inertial oscillations in the upper ocean during the Mixed Layer Dynamics Experiment (MILDEX)
Authors: Paduan Jeffrey D. , de Szoeke Roland A. , Weller Robert A.
Published: February 2008

Surface currents in the near‐inertial frequency band were analyzed from 18‐day‐long measurements taken in October/November 1983 as part of the Mixed Layer Dynamics Experiment. The currents below two drifting platforms separated by 55 km were found to have differed in their inertial response to a frontal passage on November 1 by 10 cm s−1. Wind records from the two platforms were used to compute the predicted inertial currents with a simple slab model of the wind‐driven flow. The model currents reproduced most of the features of the observed inertial currents, including the disparity between the two locations following the November 1 frontal passage. The disparity was due to differences in the weak winds preceding the frontal passage which account for inertial currents of ∼5 cm s−1 in opposing directions at the two platforms at the time of the front. These differences, or small‐scale (∼50 km) structure in the wind field, were responsible for the disparity rather than the slight difference in the arrival time (∼2 hours) of the front at the two locations.