bluuebunny/crossref_metadata_2025 huggingface dataset:
The seasonal alongshore pressure gradient on the West Coast of the United States
Authors: Hickey Barbara M. , Pola Nancy E.
Published: February 2008

The long‐term mean steric height (0/500 dbar) data of Reid and Mantyla (1976) are added to relative monthly mean adjusted sea level data to obtain a seasonal time series of “quasi‐absolute” large‐scale (>300 km) sea surface elevation along the west coast of the United States from 48°N to 33°N. North of 38°N, the elevation slope reverses sign seasonally so that the resulting pressure gradient force is southward from October to June and northward from July to September. South of 38°N, the pressure gradient force is northward except during January at all latitudes and during February in the interval from 38°N to 35°N. Maximum northward force occurs during August and September at all latitudes. The relative contributions to sea level elevation slope by seasonal heating and cooling, freshwater effluent effects, the alongshore component of coastal wind stress, and deep‐ocean currents are investigated. Both seasonal heating and cooling and freshwater contributions to large‐scale elevation slope are relatively insignificant (<10% in every month) at all latitudes. Wind stress forcing (determined with the barotropic, steady, frictional model of Csanady (1978)) is significant north of Point Conception (35°N) for both the long‐term mean slope and its seasonal oscillation. Remote contributions are particularly important in the Pacific Northwest. South of San Francisco (38°N), empirical evidence suggests that deep‐ocean currents contribute significantly to coastal elevation slope in summer and fall and in the mean. Deep‐ocean currents may also affect elevation slope along the whole coast during spring, causing elevated sea level toward the north.
The Atmospheric Lifetime Experiment: 3. Lifetime methodology and application to three years of CFCl3data
Authors: Cunnold D. M. , Prinn R. G. , Rasmussen R. A. , Simmonds P. G. , Alyea F. N. , Cardelino C. A. , Crawford A. J. , Fraser P. J. , Rosen R. D.
Published: February 2008

Observations of the chlorofluorocarbon CFCl3obtained several times daily over the period July 1978 to June 1981 at Adrigole, Ireland (52°N, 10°W); Ragged Point, Barbados (13°N, 59°W); Point Matatula, American Samoa (14°S, 171°W); and Cape Grim, Tasmania (41°S, 145°E) are reported. In addition, observations at Cape Meares, Oregon (45°N, 124°W) are given for the period January 1980 to June 1981. On January 1, 1980, the average mixing ratio of CFCl3in the lower troposphere is estimated to have been 168 pptv, and this is calculated to have been increasing 5.7% annually. An optimal estimation procedure for deriving the atmospheric lifetime of CFCl3by using a nine‐box two‐dimensional model of the atmosphere is described. In this procedure, model parameters are estimated based upon minimizing the differences between the temporal trends observed and those calculated in the two‐dimensional model. Assuming that the only destruction of CFCl3occurs in the stratosphere, the lifetime, on January 1, 1980, estimated by the trend technique isyears; the lifetime estimated from the global inventory of CFCl3isyears. The maximum likelihood current lifetime estimate obtained by combining the estimates from both analysis techniques is 78 years.
On the temporal increase of tropospheric CH4
Authors: Ehhalt D. H. , Zander R. J. , Lamontagne R. A.
Published: February 2008

The available data on the tropospheric CH4 mixing ratio in the northern hemisphere are examined for a possible trend, with the following result: There was no or little increase between 1948 and 1965 as evidenced by IR measurements of the atmospheric CH4 column density. Between 1965 and 1975 there appears a weak increase in tropospheric CH4 at an average rate of about 0.5%/yr, as suggested by independent sets of CH4 measurements. Between 1978 and 1980 a CH4 increase of 1 to 2%/yr has been observed by several laboratories. The overall trend resulting for the past 30 years is subject to a fair amount of uncertainty.
A stochastic modeling approach to the fine sediment budget of the New York Bight
Authors: Clarke Thomas L. , Swift Donald J. P. , Young Robert A.
Published: February 2008

A stochastic model of fine sediment transport on the continental shelf is modified to incorporate the effects of storm flows. The model, based on surface gravity wave resuspension, now includes transport by both tides and episodic storm flows. Effects of gravity wave/storm flow correlation as deduced from near bottom current meter measurements are also included. Sediment dispersion is significantly faster when the effects of storm flows are included. The effects of the gravity wave/storm flow correlation and the regional net flow pattern are small. The model is solved numerically for equilibrium dispersal patterns for sediment entering at estuary inlets bordering the New York Bight region. Additional dispersal patterns are found for upcoast and downcoast sources as well as the dredge spoil dump site. Combinations of these dispersal patterns are least squares fit to the observed fine sediment distribution in the New York Bight to evaluate the magnitudes of the sources of sediment; negative source magnitudes are interpreted as sediment sinks. The results are consistent with other estimates of sediment sources and sinks in the New York Bight.
Kinetics and mechanism of the oxidation of S(IV) by ozone in aqueous solution with particular reference to SO2 conversion in nonurban tropospheric clouds
Authors: Maahs Howard G.
Published: February 2008

The kinetics of S(IV) oxidation by ozone in aqueous solution have been studied at 10°C and 25°C in the pH range 3.0 to 6.2 by using stopped‐flow spectrophotometry. The rate data are empirically correlated by r = (k1 + k2 10pH)[S(IV)][O3] with k1 = 4.39 × 1011 e−4131/T (±3 × 104) M−1S−1, and k2 = 2.56 × 103 e−966/T (±15)s−1 at an ionic strength of 0.01 M. Reaction rate is unaffected by incident strong UV radiation, or the presence of Mn(II) or Fe(III), but is weakly dependent on ionic strength. The present results, in comparison with reported rates of oxidation of S(IV) by hydrogen peroxide, indicate that at typical pH levels encountered in nonurban tropospheric cloud water and at representative concentrations of O3 and H2O2 in the troposphere, oxidation by O3 can be competitive with that by H2O2, or possibly even dominate. The reaction appears to proceed by other than a free‐radical process, and a reaction scheme involving direct ozone attack catalyzed by hydroxide ion is proposed. A rate expression consistent with this scheme is r = (ka + kb[OH−])[HSO3−][O3] where ka = 3.8 × 105 M−1s−1 and kb = 1.05 × 1016 M−2s−1 at 25°C. This expression correlates the present data with literature data over the pH range 1.0 to 6.2.
Albedo of soot‐contaminated snow
Authors: Chýlek Petr , Ramaswamy V. , Srivastava Vandana
Published: February 2008

We present a new model of snow containing impurities (graphitic carbon). Submicron‐sized soot particles are supposed to be distributed randomly throughout the volume. Using the mixing rule for a dielectric constant of a composite medium, we calculate the refractive index of a snow‐soot mixture. Then we obtain the single scattering albedo and the asymmetry factor. Using the delta‐Eddington approximation, we determine the reflectivity (albedo) of a snow layer in the wavelength range 0.3 μm≤λ ≤2.5 μm. The calculated spectral albedos and the deduced amounts of graphitic carbon agree well with field measurements.
Atmospheric boundary‐layer modification, drag coefficient, and surface heat flux in the Antarctic marginal ice zone
Authors: Andreas Edgar L. , Tucker Walter B. , Ackley Stephen F.
Published: February 2008

During a traverse of the Antarctic marginal ice zone (MIZ) near the Greenwich Meridian in October 1981, we launched a series of radiosondes along a 150‐km track starting at the ice edge. Since the wind was from the north, off the ocean, these radiosonde profiles showed profound modification of the atmospheric boundary layer (ABL) as the increasing surface roughness decelerated the flow. The primary manifestation of this modification was a lifting of the inversion layer with increasing distance from the ice edge by the induced vertical velocity. But there was also a cooling of the stably stratified mixed layer below the inversion and a consequent flux of sensible heat to the surface that averaged over 200 W/m2. The magnitude of this flux suggests that atmospheric heat transport plays a significant role in the destruction of ice in the Antarctic MIZ. Using the rising of the inversion and ABL similarity theory, we estimated the change in the neutral stability drag coefficient, CD, across the MIZ. CD increased from its open ocean value, 1.2×10−3, at the ice edge to 4.0×10−3 at 80–90% ice concentration. We present an equation for this dependence of drag on ice concentration that should be useful for modeling the surface stress in marginal ice zones.
The density jump across Little Bahama Bank
Authors: Luyten James , Stommel Henry
Published: February 2008

There is a discontinuity in density across the Bahama Banks. On the western side of the banks, beneath the mixed layer, isopycnals are about 100 m shallower than on the eastern side. An explanation is offered in terms of a reduced gravity layered model of an inertial western boundary current forced to flow through a channel (the Florida Straits) which is narrower than its open ocean scale width.
Lagrangian observations of an anticyclonic ring in the western Gulf of Mexico
Authors: Kirwan A. D. , Merrell W. J. , Lewis J. K. , Whitaker R. E.
Published: February 2008

This analysis documents, for the first time, the movement and velocity characteristics of an anticyclonic ring. The ring was pinched off from the Loop Current in the fall of 1980 and moved into the western Gulf of Mexico. Lagrangian measurements obtained from satellite‐tracked drifters show that typical speeds of the near‐surface currents associated with this ring are about 50 cm/s. There is also a surprising amount of higher‐frequency current fluctuations. These include diurnal and semidiurnal tides, a basin tidal resonance, and a free gravity mode.
A model for the analysis of drifter data with an application to a warm core ring in the Gulf of Mexico
Authors: Kirwan A. D. , Merrell W. J. , Lewis J. K. , Whitaker R. E. , Legeckis R.
Published: February 2008

A model developed primarily for the analysis of drifter data is discussed. The model is based on a parametric representation of the drifter velocity in terms of Monge potentials, two of which are constants following the motion of the fluid. In the application presented here, one of the potentials is taken as the frequency of rotation about a ring by a parcel. A more restricted interpretation of the velocity gradient in variant for horizontal flow is also discussed. The other potential is taken as the streamline of a parcel that is locally approximated as a conic section. For the restricted interpretation, solutions to the model equations are critically dependent on the relative sizes of the squares of the vertical vorticity and the total deformation rate. This model differs from drifter cluster models in that each drifter provides independent estimates of the vorticity and deformation rates. Application is made to path data from three drifters that were seeded in a warm core ring in the Gulf of Mexico in November 1980. The model provided estimates of the ring translation and swirl velocities along with the ring geometry. The analysis showed that the ring was persistently elliptical with the major axis aligned in the east‐west direction. A satellite infrared photo on January 21,1981, confirmed this orientation.
Spectral albedos of sea ice and incident solar irradiance in the southern Beaufort Sea
Authors: Grenfell Thomas C. , Perovich Donald K.
Published: February 2008

Spectral albedos and incident spectral irradiances have been measured over the wavelength range 400 to 2400 nm on the sea ice near the Naval Arctic Research Laboratory (NARL) at Pt. Barrow, Alaska. The observation interval extended from mid‐May, when the ice was still relatively cold, until mid‐June, when summer melting was fully established. The temporal dependence of albedo for the available surface types was obtained over this time interval showing a general decrease from snow and snow‐covered ice to blue ice and melt ponds. Data were also obtained for glacier ice on the Athabasca glacier, for melting lake ice, and for certain other nonice surfaces in the vicinity of NARL. Snow and ice albedos are characteristically highest at visible wavelengths, decreasing strongly in the infrared because of the increase in absorption by ice and water. Local maxima in the spectra correspond to minima in the ice and water absorption. Variations in albedo are due primarily to differences in the vapor bubble density, crystal structure, and free water content of the upper layers of the ice. Incident spectral shortwave radiation was measured as a function of cloudiness, and the optical thickness of arctic clouds is significantly less than the thickest clouds at lower latitudes. The decrease of the infrared component relatiave to the visible portion of the irradiance with increasing cloud cover is determined. This can give rise to an increase in wavelength‐integrated albedos of as much as 15%. Using the present data, a graphical method is outlined by which visible near‐infrared satellite imagery can be used to distinguish among melt ponds, open leads, and other spring and summer sea ice surface types.
The carbonate chemistry of Grand Bahama Bank waters: After 18 years another look
Authors: Morse John W. , Millero Frank J. , Thurmond Valerie , Brown Elissa , Ostlund H. G.
Published: February 2008

Major features of the chemistry of northern Grand Bahama Bank waters found in 1981 were similar to those found by Broecker and Takahashi in 1962 and 1963. Measured variations in salinity and extent of CaCO3 removal are close to the same. Our findings indicate a more complex salinity distribution on the northern banks, probably resulting from transport of high salinity waters from the south and higher PCO2 values in the high salinity waters. Inorganic 14CO2 measurements made in this study can be used to calculate very approximate residence times of water on the bank. There is general agreement with the values previously determined by Broecker and Takahashi. Ship, aerial, and satellite observations indicate that “whitings” are not randomly distributed over the bank. They form a halo around the northern and western flanks of the high salinity waters (S greater than 40). The rate of CaCO3 removal is about 1.5 times faster in the waters where the whitings are common than in the high salinity waters. Even though our analytic precision was over 80 times greater than the change predicted in alkalinity if whitings precipitate directly from seawater, no differences could be found between whiting and adjacent waters. In our opinion, the major features responsible for creating whitings, controlling their distribution, and determining CaCO3 removal rates on the Grand Bahama Bank remain largely unresolved.
Internal tide and solitons on the Scotian Shelf: A nutrient pump at work
Authors: Sandstrom H. , Elliott J. A.
Published: February 2008

During a measurement program on the Scotian Shelf off Nova Scotia, large amplitude internal waves were observed in the vicinity of the shelf edge. Some were identified positively as solitons. The observations provide insight into the soliton generation process and explain the role they play in the transfer of energy from tides to ocean mixing. It is found that the shoreward propagating energy in the baroclinic tide, which is generated at the shelf edge, is dissipated by way of the large‐amplitude, short internal waves. Based on observed dissipation rates of solitary waves, it is concluded that the associated amount of mixing is sufficient to supply the required nutrients to the euphotic zone.
On small‐scale horizontal variations of salinity in first‐year sea ice
Authors: Tucker W. B. , Gow A. J. , Richter J. A.
Published: February 2008

Measurements of salinity over horizontal distances of 38 to 76 cm in a thick first‐year ice sheet have revealed significant differences. A maximum salinity difference of 2‰ was observed between ice core segments from the same depth. The mean standard deviation for 10‐cm thickness increments through the 2.0‐m ice sheet was 0.39‰ between the five closely spaced cores. The most likely mechanism for these significant differences in salinity over short distances is differential brine drainage in the ice sheet due to varying locations of brine drainage channels. A simple one‐dimensional model which assumes a normally distributed arrangement of brine drainage channels provides results consistent with the horizontal differences observed.
Microwave emission from high Arctic sea ice during freeze‐up
Authors: Hollinger J. P. , Troy B. E. , Ramseier R. O. , Asmus K. W. , Hartman M. F. , Luther C. A.
Published: February 2008

A cooperative sea ice remote sensing experiment was conducted in the eastern Beaufort Sea and Mould Bay area during the freeze‐up period in October 1981. Airborne millimeter‐wave imagery at 90, 140, and 220 GHz, and nadir microwave radiometric measurements at 19, 22, and 31 GHz, were made from a U. S. Naval Research Laboratory aircraft, while the Canadian Atmospheric Environment Service conducted an extensive concurrent surface measurement program. This study demonstrates for the first time the high‐resolution capability of 90 GHz to investigate detailed ice morphology and to define ice types. The 140 and 220 GHz imagery is the first ever made of sea ice at these high frequencies. Emissivities are determined for young ice, second‐year ice (SY), multiyear ice (MY), new ice, old shorefast ice, and open water. The young ice exhibits the emissivity typical of first‐year (FY) ice types, i.e., near unity and independent of frequency. The emissivities of new ice and open water increase with frequency, and that of MY ice decreases with frequency. Those of SY ice and old shorefast ice, measured here for the first time, also decrease with frequency but are larger in value than the MY emissivity. Ice type discrimination is optimum at 90 GHz, i.e., the spread in microwave signature between FY ice and old ice (SY and MY) is greatest at 90 GHz. The MY emissivity is lower than that of open water at both 90 and 140 GHz. The measurements presented here provide a basis for development of algorithms to exploit the potential of the Mission Sensor Microwave/Imager (SSM/I) to be launched on a Defense Meteorological Satellite in 1985 and, in particular, the 85.5‐GHz SSM/I channels for ice type, concentration, and edge determination.
The increase in oceanic carbon dioxide and the net CO2 flux into the North Atlantic
Authors: Roos Marita , Gravenhorst Gode
Published: February 2008

In the present work the differences between the pCO2 in the sea surface water and the atmospheric CO2 mixing ratio were determined on the basis of measurements of Meteor expedition 32 in the North Atlantic in 1973. These Meteor measurements were complemented by a compilation of CO2 data that has been available to us on the North Atlantic since the beginning of this century. A thorough evaluation of these data shows that, like the increase of the CO2 mixing ratio in the atmosphere, there is also a general increase of pCO2 in the surface water of the North Atlantic. Although the CO2 differences across the air‐sea interface have been measured by various methods since 1903, they can still be compared and, at the same time, be used to derive their geographical distribution on the North Atlantic. Based on these data, net CO2 fluxes of 0.16×1015 g C a−1 from the atmosphere into the North Atlantic between the equator and 40°N and of 0.45×1015 g C a−1 north of 40°N are derived. The total net CO2 uptake of 0.6×1015 g c a−1 corresponds to 13% of the present global industrial CO2 emission per year.
Bottom‐boundary condition for nonequilibrium transport of sediment
Authors: Cheng Kwokming James
Published: February 2008

This paper formulates a generalized bottom‐boundary condition for nonequilibrium transport of sediment in terms of two parameters: the deposition velocity and the equilibrium bottom concentration. Theoretical expressions for the two parameters are derived. Analytical solution to the sediment transport equation, using the generalized bottom‐boundary condition, is also given. Finally, a number of available formulations of the bottom condition are reviewed and shown to be special cases of this generalized one.
Island wakes in shallow coastal waters
Authors: Wolanski E. , Imberger J. , Heron M. L.
Published: February 2008

Rattray Island, northeast Australia, is 1.5 km long, 300 m wide, and lies in well‐mixed water approximately 25 m deep. Its long axis is inclined at about 60° into the direction of the dominant semidiurnal tidal current. The length of the wake in the lee of the island, as documented by aerial photographs and satellite imagery, appears to equal that of the wake behind a flat plate in a two‐dimensional flow at a Reynolds number of about 10. However, current metering, drogues measurements, and temperature mapping indicate internal wake velocities much greater than would be consistent with such a simple low Reynolds number model. Further, estimates of the turbulent eddy coefficient suggest an effective Reynolds number more in the vicinity of 103. To reconcile these observational differences and to explain the observed upwelling in the core of the wake, an Ekman pumping model is proposed. It is postulated that the Ekman benthic boundary layer driven by rotation in the wake allows the vertical vorticity introduced into the water at the tip of the island at the point of separation, to be negated by the vorticity of opposite sign introduced at the bottom. Further, it is shown that a large fraction of the kinetic energy of the upstream flow facing the island is used to drive the wake eddies, leading to the conclusions that the trapping of water in the lee of islands greatly increases head losses on continental shelves with numerous islands, coral reefs, and rock outcrops.
The simulated response of an upper‐ocean density front to local atmospheric forcing
Authors: Adamec David , Garwood Roland W.
Published: February 2008

Four numerical experiments with different atmospheric forcing are considered to investigate a variety of transient responses of an upper‐ocean density front similar to the Maltese front (south of Sicily) in an embedded mixed layer—ocean circulation model. Of particular interest is a case that simulates forcing observed by O. M. Johannessen (unpublished report, 1975): in May 1971, measurements of the Maltese front were being taken in calm weather, and then the wind suddenly increased to 10–15 m s−1 down the front. For this forcing the model result is consistent with the observations predicting steepening of the frontal interface, spreading of the surface isopycnals, and very little horizontal displacement of the surface front. However, the model predicts too much mixed‐layer deepening and fails to predict the observed strengthening of the along‐front flow. Three additional experiments are considered to assess the effects of a change in the wind direction and the inclusion of a surface buoyancy flux. The inclusion of a diurnal surface buoyancy flux produces a very different response from the simulations with no buoyancy flux: when the surface buoyancy flux is negative, the mixed layer reforms at a shallow depth, resulting in much higher adverting velocities and subsequently larger displacements of the surface front. The negative buoyancy flux can effectively protect the subsurface structure with a shallow, stable surface layer; it also decouples the deeper frontal processes from the surface mixed‐layer processes.
Low frequency sea level variability in the vicinity of the East River tidal strait
Authors: Wilson Robert E. , Wong K.‐C. , Filadelfo Ronald
Published: February 2008

The East River is a narrow tidal strait connecting Long Island Sound with the lower Hudson Estuary; the Sound and Estuary both communicate with the New York Bight. Subtidal fluctuations in sea level difference between the ends of the strait which are coherent with barotropic flow through the strait are produced mainly by direct setup in the Sound and Estuary and by sea level fluctuations (primarily wind forced) in the Bight. Approximately 70% of the variance in subtidal sea level difference can be accounted for by the two components of wind stress. The direction of dominant wind forcing (wind stress direction producing maximum response) varies considerably with frequency. Response functions relating sea level difference to wind stress components computed for 128 day series for sea level and winds allow us to interpret the direction of dominant forcing in terms of the relative contributions of direct setup and sea level fluctuations in the Bight.
Aircraft and satellite measurement of ocean wave directional spectra using scanning‐beam microwave radars
Authors: Jackson Frederick C. , Walton W. Travis , Baker Paul L.
Published: February 2008

A microwave radar technique for remotely measuring the vector wave number spectrum of the ocean surface is described. The technique, which employs short‐pulse, noncoherent radars in a conical scan mode near vertical incidence, is shown to be suitable for both aircraft and satellite application. The technique has been validated at 10 km aircraft altitude, where we have found excellent agreement between buoy and radar‐inferred absolute wave height spectra.
A review of satellite altimeter measurement of sea surface wind speed: With a proposed new algorithm
Authors: Chelton Dudley B. , McCabe Patrick J.
Published: February 2008

The scheduled February 1985 launch of a radar altimeter aboard the U.S. Navy satellite Geosat has motivated an in‐depth investigation of wind speed retrieval from satellite altimeters. The accuracy of sea surface wind speed estimated by the Seasat altimeter is examined by comparison with wind speed estimated by the Seasat scatterometer. The intercomparison is based on globally distributed spatial and temporal averages of the estimated wind speed. It is shown that there are systematic differences between altimeter and scatterometer wind speed estimates. These differences are traced to errors in the Seasat altimeter geophysical data record wind speed algorithm. A new algorithm is proposed which yields consistent estimates from the two satellite sensors. Using this new algorithm, the rms difference between spatial and temporal averages of the two wind speed estimates is less than 1 m/s, and their correlation is greater than 0.9.
The Transient Tracers in the Ocean (TTO) program: The North Atlantic Study, 1981; The Tropical Atlantic Study, 1983
Authors: Brewer Peter G. , Sarmiento Jorge L. , Smethie William M.
Published: February 2008

The scientific papers here collected result from the Transient Tracers in the Ocean (TTO) program. The two parts of this major geochemical and physical oceanographie expedition took place in the North Atlantic Ocean in 1981 and in the Tropical Atlantic in 1983 on the research vessel Knorr of the Woods Hole Oceanographie Institution.

The expeditions, sponsored by the National Science Foundation and the U.S. Department of Energy (North Atlantic only), were designed to observe the passage of man‐made geochemical tracers into the interior of the ocean. The foundations for such an experiment were laid in the 1972‐1978 GEOSECS program. Here, for the first time, a systematic survey revealed the penetration into the thermocline and deep ocean of the products of man's military/industrial activities, principally tritium and carbon‐14 resulting from atmospheric testing of nuclear weapons, which terminated with the nuclear test ban treaty in 1962.
A meridional 14C and 39Ar section in northeast Atlantic deep water
Authors: Schlitzer Reiner , Roether Wolfgang , Weidmann Urs , Kalt Peter , Loosli Heinz Hugo
Published: February 2008

14C, 39Ar, and complementary hydrographic and nutrient data are presented for deep water below 2500 m depth, from stations along a meridional section (8°S to 45°N) through the Romanche Trench and along the deep northeast Atlantic basins (F/S Meteor, cruise 56, leg 5). The large‐scale 14C distribution along the section is resolved at the 14C data precision of ±2‰. Bottom water Δ14C decreases by 6‰ from the equator to 45°N, and farther up there is a weak Δ14C minimum (−123‰) over much of the section. The 14C data are interpreted as giving a turnover time of about 30 years for the waters below the depth of the 14C minimum (∼4250 m). It is found that water of 1.50±0.05°C potential temperature enters the East Atlantic from the west through the Romanche Trench (sill depth about 4000 m), and a preliminary value for the inflow rate of 3.6×106 m3/s is deduced. This rate greatly exceeds estimated deep inflow rates through the Vema fracture zone or across the northern boundary of the East Atlantic. 39Ar data that cover an entire deep‐ocean circulation system are presented for the first time. The observed 14C and 39Ar distributions are mutually consistent. Transit times from the source regions to the equator for water from northern and southern deepwater sources are estimated to be about 170 and 105 years, respectively, and the 39Ar concentration of young Antarctic Bottom Water is deduced as 60±7% modern. The 39Ar‐14C correlation in the ocean appears to be affected by mixing of waters of different age and by more efficient raising of 39Ar in the deepwater formation processes.
On the response of the equatorial thermocline in the Atlantic Ocean to the seasonally varying trade winds
Authors: Weisberg R. H. , Tang T. Y.
Published: February 2008

Measurements made during the Seasonal Response of the Equatorial Atlantic experiment in 1983, when the easterly trade winds near the equator ceased and then intensified as part of their annual cycle, show a sequence of events leading to an adjusted thermocline. Both the duration and extent of the downwelling and upwelling associated with the adjustment process were zonally inhomogeneous along the equator. An analytical reduced gravity model was driven by a hierarchy of easterly wind stress forcing functions representative of the Atlantic to compare the integral nature of the forced long‐wave responses with the observations. Qualitative agreement was found with upwelling and downwelling sequences within the forced region increasing to the east as observed. Apparent model propagation speeds differed significantly from the prescribed model wave speeds within the forced region owing to the growth parameters of the winds, and boundary reflections distorted the responses to the east of the forced region. The resulting interference patterns tended to separate the region 0°–10°W along the equator from the African coast as one of maximum upwelling.
Influence of gas transfer on the CO2 uptake by the ocean
Authors: Memery Laurent , Merlivat Liliane
Published: February 2008

The most recent models dealing with CO2 uptake by the ocean divide the ocean by latitude, but they do not take into account the influence of the different wind regimes on the CO2 fluxes across the air‐Water interface. However, new gas exchange experiments run in wind tunnels have shown a great enhancement of the transfer velocity at high wind speeds as a result of the development of breaking waves. A study of sensitivity of two different models (Siegenthaler outcrop box diffusion model and Takahashi‐Azevedo inclined box diffusion model) to an increase of the CO2 transfer velocity at high latitudes (outcrop regions of the deep ocean) is undertaken. It is shown that the variations in the transfer velocity with latitude must be taken into account.
Wintertime convection in warm‐core rings: Thermocline ventilation and the formation of mesoscale lenses
Authors: Schmitt Raymond W. , Olson Donald B.
Published: February 2008

Large heat losses from warm‐core ring 82B during February, March, and April 1982 formed a 400‐m‐thick thermostad in the center of the ring. Two different models were constructed to simulate the formation of the thermostad water mass properties: a one‐dimensional vertical model forced with a meteorological time series and a volumetric mixing model with climatological input. Both models indicate that a flux of slope water into the ring is necessary to yield the observed thermostad salinities. The subsequent slow decay of the ring core in the slope water suggests that such winter‐convected rings can easily maintain the “warm band” water identified by Wright and Parker (1976). The large loss of core water during interactions with the Gulf Stream suggests that the reabsorption of such winter‐cooled warm rings is an important source of high‐salinity, high‐oxygen anomalies in the main thermocline of the Sargasso Sea. The volume of water in a typical ring reabsorption is sufficient to generate many (>20) intrathermocline eddies with T‐S properties close to those of recently reported lenses. This suggests that many of these small eddies are much more local in origin and may be more highly dissipative than has previously been suggested. An estimate of the flux of high‐salinity, high‐oxygen water into the main thermocline by this mechanism leads to ventilation at a rate that is a significant fraction of the Ekman pumping at these density levels. Thus the reabsorption of winter‐cooled warm‐core rings by the Gulf Stream is an important eddy ventilation mechanism for the Sargasso Sea.
Frictionally induced circulations and spin down of a warm‐core ring
Authors: Flierl Glenn R. , Mied Richard P.
Published: February 2008

Meridional motion driven by kinematic viscosity v and thermal diffusivity k within a warm‐core ring is examined. An analytic quasi‐geostrophic model is constructed that shows that the vertical mixing of heat or momentum is ineffective in driving secondary motion. Single‐celled meridional flows will occur within the ring whenever the Prandtl number Pr = vh/κh is not equal to 1. When Pr is greater than 1, the flow is up in the ring core, while Pr less than 1 causes downward motion at ring center. A numerical primitive equation model leads to qualitatively identical results but shows that the secondary flow is not long‐lived when Pr is less than 1, decaying within 2 months, while in the Pr greater than 1 case the flows are still vigorous at the end of the experiment (90 days).
Warm water cells in the North Water, Northern Baffin Bay during winter
Authors: Steffen Konrad
Published: February 2008

Sea surface temperatures above the freezing point of seawater (−1.8°C) were observed in the North Water during winter and early spring. The result indicates a possibility of upwelling warm water, presumably of Atlantic origin, brought from lower depths to the surface. The warm water temperatures ranged from −1.7° to −0.1°C. The highest occurrence frequency lay in the temperature interval from −1.0° to −0.8°C. Most warm water cells were found along the Greenland coast in Smith Sound, Lady Ann Strait, and Barrow Strait. They occurred most frequently in Smith Sound, west of Cape Alexander. The highest temperatures of −0.1°C occurred, however, south of Cape Alexander. The occurrence frequency and the total area of warm water patches decreased toward spring. The predominantly northerly wind that is channeled in Smith Sound accounts for a mean ice drift of approximately 17 km d−1. This ice drift causes an ice divergence in Smith Sound and along the Greenland coast. The existence of warm water areas can be explained by the strong northerly wind resulting in a Coriolis force that induces coastal upwelling. The wind‐induced offshore transport of 3.5×105 m3 s−1 in the North Water, compensated by the upwelling of Atlantic Baffin Bay water (0°C) along the Greenland coast, will suffice to keep 10% of the North Water ice free. The combination of ice divergence and forced convection of warm water can be considered as a prime cause of the polynyas in the North Water.
A granular‐fluid model for steady intense bed‐load transport
Authors: Hanes Daniel M. , Bowen Anthony J.
Published: February 2008

The mechanics of collisional grain flows are applied to the intense bed‐load transport of sediment. The velocity distribution and grain transport are determined analytically without any freely adjustable parameters. The flow is modeled as two fluid regions with continuous stress, velocity, and granular concentration overlying a stationary bed: a collision‐dominated granular‐fluid region and a wall‐bounded turbulent‐fluid shear region with saltating grains. A simple kinematic model for the saltation of grains is developed to predict the grain transport in the saltation zone and to provide the upper boundary conditions for the granular‐fluid region. The velocity in the granular‐fluid region is found to be approximately proportional to the applied shear stress raised to the 3/2 power under the assumption of a linearly varying volume concentration. The grain flux and energy dissipation are proportional to the applied shear stress raised to the 5/2 power. When compared with observations and previous models, the present formulation predicts significantly greater transport at extremely high stresses. Calculations of the energy dissipation are consistent with previous transport models that are based on energetics arguments.
Relations between sea level, thermocline depth, heat content, and dynamic height in the tropical Pacific Ocean
Authors: Rebert J. P. , Donguy J. R. , Eldin G. , Wyrtki K.
Published: February 2008

The use of combined information from expendable bathythermograph and sea level observations for ocean monitoring requires the establishment of relations between sea level, thermocline depth, heat content, and dynamic height. Sea level fluctuations are a good measure of thermocline depth fluctuations in the tropical Pacific between about 15°N and 15°S and allow the determination of changes of upper‐layer volume. Sea level is also a good measure of heat content, and useful correlations extend to higher latitudes. Dynamic height and sea level fluctuations agree only in those areas where the thermal structure resembles a two‐layer system very well, and good correlations are restricted to a narrower area. The combination of bathythermograph and sea level observations will allow a better mapping of the changes of thermocline topography, heat content, and dynamic height for the monitoring of climatic changes in the tropical Pacific.
Fine‐structure variability observed in CTD measurements from the central equatorial Pacific
Authors: McPhaden M. J.
Published: February 2008

Conductivity, temperature, and depth data from the 15 quasi‐monthly cruises of the Hawaii‐Tahiti Shuttle Experiment are used to document fine‐structure variability in the upper 400 m of the central equatorial Pacific. The analysis reveals the existence of anomalously strong temperature and density variations on 0(1–10 m) vertical scales concentrated in the high mean shear zones of the equatorial current system and in the thermostad. These are regions where microscale measurements also indicate intense turbulent activity. The implication of this spatial correspondence between large‐, fine‐, and microscale signals is that there may be a cascade of energy from the largest to the smallest scales of variability that is mediated by fine‐structure processes. The highly structured fine‐scale signal suggests that the cascade would be most pronounced and persistent on certain density surfaces that lie within the regions of highest mean shear. Other processes, such as wind stirring, air‐sea buoyancy exchange, and intrusions, also contribute to the generation of fine‐structure variability and mixing at equatorial latitudes. There is evidence, for example, that intrusions across the sharp equatorial salinity front in the upper 150–200 m account for 10%–20% of the fine‐structure temperature variance and more than 50% of the fine‐structure salinity variance. The dominant vertical scale of these intrusions appears to be ≲10 m and the cross‐frontal scale < 100 km. A simple model calculation of cross‐frontal mixing indicates that they are important in transferring heat and salt laterally across the front. Intrusions in the vicinity of the Equatorial Undercurrent core may support salt fingering; hence they may contribute to vertical transports of salt and heat in a region where turbulent mixing is weak.
Convergence in the equatorial surface jets of the Indian Ocean
Authors: Reverdin G.
Published: February 2008

Twenty‐one surface drifters have been deployed in the equatorial Indian Ocean since 1979. Their trajectories are used to estimate the near‐surface meridional convergence in eastward surface jets, which is found to be typically of the order of −0.8×10−6 s−1. A 2.5‐year time series of currents and temperature profiles not made simultaneously, but in the same area, at Gan (73°E, 0°30′S; Knox (1976)), is also analyzed. The balance of forces averaged vertically in the mixed layer is consistent with a horizontal convergence of the order of −0.3×10−6 s−1, when the surface currents are eastward. The difference between the surface estimate based on the buoy trajectories and the other estimate is consistent with the expectation that convergence should be maximum near the surface. Zonal velocities are also larger near the surface, with a mean vertical shear of 0.4×10−2 s−1 when mixed layers are deeper than 60 m.
A simple model of estuarine subtidal fluctuations forced by local and remote wind stress
Authors: Garvine Richard W.
Published: February 2008

Observations of estuarine low subtidal sea level and current fluctuations have often shown domination by the remote effects of the wind, acting on the adjacent coastal ocean, over the local surface stress, acting on the estuary itself. The remote effects are transmitted to the estuary by impressment on its mouth of sea level change induced by the onshore component of coastal Ekman transport and become increasingly dominant as the frequency decreases. A simple, barotropic model is developed to investigate the joint action of these two wind forcing mechanisms. The relative shortness of most estuaries relative to low subtidal estuarine wavelengths explains the dominance of the remote effect for both sea level and barotropic current fluctuations in the estuary. For the same reason, however, surface slope is dominated by local wind setup. For an estuary with axis nearly parallel to the coast the two effects will operate either in concert or in opposition, depending on hemisphere and orientatipn of the estuary axis relative to the coast. For the geometries of both Chesapeake Bay and the Delaware Estuary the model predicts opposition with the remote effect dominant at lower frequencies, consistent with recent observations.
HE and RN gas exchange experiments in the large wind‐wave facility of IMST
Authors: Jähne B. , Wais T. , Memery L. , Caulliez G. , Merlivat L. , Münnich K. O. , Coantic M.
Published: February 2008

In a collaboration between the Laboratoire de Géochimie Isotopique (Centre d'Etudes Nucléaires, Saclay), the Institut de Mécanique Statistique de la Turbulence (IMST, Marseille), and the Institut für Umweltphysik (Heidelberg), for the first time gas exchange experiments have been carried out in the large IMST wind‐wave facility. The experiments included simultaneous measurements of Rn and He gas exchange rates, wave slope measurements at four fetches, and bubble measurements. Compared with transfer velocities measured previously in smaller tunnels, our results are considerably lower. This effect can be explained qualitatively by differences in the wave field, which must be taken into account as an important parameter for gas exchange. Wave breaking, starting at 12 m/s wind, was not intense. Consequently, only low bubble densities are obtained, not significantly enhancing gas exchange.
Vertical distribution of feeding and particle‐selective transport of 137Cs in lake sediments by lumbriculid oligochaetes
Authors: Krezoski John R. , Robbins John A.
Published: February 2008

Lumbriculid oligochaetes are an important member of the conveyor belt deposit‐feeding species responsible for advective reworking of profundal sediments in the Great Lakes. These threadlike worms ingest sediments over a range of depths (0–5 cm) and deposit gut contents at the sediment surface. This action results in a depth‐dependent particle advection rate which can be related to the distribution of their feeding. In this study, two replicate microcosms of rectangular cross section (3×5 cm) containing evenly spaced (1 cm) thin layers (0.5 mm) of sediment labeled with gamma‐emitting 137Cs were inoculated with the lumbriculid Stylodrilus heringianus at a density of ∼7.9×104 m−2 (10°C). The subsequent amount of tracer lost from each layer as well as the downward movement of the layers were determined by peiodically scanning the length of the cells with a well‐collimated gamma detector system. During the course of the 600‐hour experiment, 137Cs activities decreased only in layers between 0 and 6 cm depth. These decreases were accompanied by the appearance of a new layer at the sediment surface. Between 80 and 90% of the activity lost from the underlying layers appeared in the emergent surface peak, thus indicating that subsurface defecation was minor aspect of conveyor belt transport. Decreases in 137Cs activity within layers were consistent with first‐order kinetics with a maximum loss rate of about 0.08% hour−1. The vertical distribution of the rate constant was very nearly Gaussian with the maximum at 3.3 cm and a spread (SD) of 1.4 cm. The rate of layer burial decreased monotonically but nonlinearly with sediment depth from an extrapolated surface value of about 1.8×10−2 mm h−1. A model based on conservation of mass was developed which relates the tracer feeding distribution to the velocity distribution assuming that the distribution of mass removed through feeding was proportional to the amount of tracer removed. The model takes rigorous account of depth‐dependent porosity and provides an excellent description of the velocity distributions if the transfer of 137Cs is taken to be 1.67 times the mass transfer rate. This factor, termed the feeding selectivity factor, is attributed to the selection of fine particles by worms and is important in models describing trace and contaminant diagenesis in sediments reworked by conveyor belt species.
The dissipation of kinetic energy in a warm‐core ring
Authors: Lueck Rolf , Osborn Thomas
Published: February 2008

Profiles of the rate of viscous dissipation of kinetic energy in a Gulf Stream warm‐core ring show large rates in the thermocline and in the entrainment region near the edge of the ring. The thermostad has very low levels of dissipation except where that region is in contact with the Gulf Stream. Dissipation rates in the thermocline are independent of the large scale vertical shear and are consistent with the concept of near‐inertial wave trapping by the ring's geostrophic shear. Near the edge, to depths of 1000 m, turbulence is associated with entrainment and interleaving. The e‐fold decay scale for the dissipation of the ring's total energy is 2 to 3 years, but is only 140 days for the kinetic energy, so energy conversion from potential to kinetic must be occurring on time scales of 10 to 30 days. The vertical eddy diffusivity of the ring is 0.1 × 10−4 m2/s except in the thermostad where it is smaller by approximately a factor of 10. The eddy viscosity is more than 10 × 10−4 m2/s; hence tubulent diffusion is relaxing the velocity field faster than the thermal field.