bluuebunny/crossref_metadata_2025 huggingface dataset:
CO2‐induced change in a coupled ocean‐atmosphere model and its paleoclimatic implications
Authors: Manabe Syukuro , Bryan Kirk
Published: February 2008

The climatic effects of very large changes of CO2 concentration in the atmosphere are explored using a general circulation model of the coupled ocean‐atmosphere system. As a simplification the model has an annual mean insolation and a highly idealized geography, A series of climatic equilibria are obtained for cases with ½, 1/√2, 1, 2, 4, and 8 times the present CO2 concentration in the atmosphere. The results from these six numerical experiments indicate the climatic signatures of large CO2 changes in the atmosphere and in the abyssal and surface waters of the ocean. As the CO2 concentration in the model atmosphere increased from 1 to 8 times the normal value, the meridional gradient of surface air temperature decreased, while that of upper tropospheric temperature increased in agreement with the results of earlier CO2 climate sensitivity studies. However, the intensity and latitudinal placement of the atmospheric jet hardly changed. Despite the reduction of meridional temperature gradient, the meridional density gradient of water at the ocean surface changed little because of the increase of thermal expansion coefficient of seawater with increasing temperature. Thus the intensity of thermohaline circulation in the ocean model does not diminish as expected in the range from 1 to 8 times the normal atmospheric CO2 concentration. As was shown in an earlier study, the CO2‐induced changes in the deep sea follow the change of sea surface temperature in high latitudes and thus are much larger than the globally averaged changes of sea surface temperature. The model predicts that the area mean rates of precipitation, evaporation, and runoff increase with increasing CO2 concentration in the atmosphere. The latitudes of the arid zone and the high surface pressure belt in the subtropics are almost constant in the entire range of 1–8 times normal CO2. In general, the climatic signature obtained from the model appears to be consistent with a CO2 hypothesis for the climatic changes in the Cenozoic with the following exception: the tropical sea surface temperature in the model has a small but significant increase with increasing atmospheric CO2 concentration, while tropical sea surface temperature as deduced from the isotopic record appears to have no systematic trend during the Tertiary. It is found that the climate corresponding to one‐half normal CO2 is markedly different from the normal and high‐CO2 cases. Sea ice extends to middle latitudes, and the thermohaline circulation in the model ocean loses its intensity and is largely confined to an area between the sea ice margin and the equator. The poleward heat transport by ocean currents is very small in high latitudes, markedly reducing the surface air temperature there. It is suggested that a similar process, which enhances the positive albedo feedback effect of sea ice, played a key role in reducing surface air temperatures over the North Atlantic during the last glacial maximum.
Internal wave dissipation under sea ice
Authors: Morison James H. , Long Charles E. , Levine Murray D.
Published: February 2008

The dissipation of internal wave energy in the turbulent boundary layer under pack ice is determined using a time‐varying boundary layer model with an eddy coefficient closure scheme. The magnitude of the eddy coefficient is determined by the ice drift velocity, which is assumed greater than the rms water velocity induced by internal waves. The Arctic Ocean internal wave velocity spectrum is represented by a line spectrum with 44 rotary frequency components. The energy at a given frequency is set equal to the energy in a band about the frequency in the continuous spectrum. The dissipation spectrum is found to have an ω−2 shape. For an internal wave energy level representative of Arctic Ocean conditions (energy parameter r equal to 50 m2 cph) the total dissipation is 0.16 mW m−2. This corresponds to a dissipation time scale of 32 days and suggests that underice dissipation is important. The surface boundary layer dissipation process is unique to ice‐covered regions, and the predicted amount of dissipation appears to be great enough to explain earlier observations that the internal wave energies in the Arctic Ocean are low compared to internal wave energies measured in ice‐free oceans.
Formation of thermoerosional niches into frozen bluffs due to storm surges on the Beaufort Sea coast
Authors: Kobayashi Nobuhisa
Published: February 2008

An analysis is made of the formation of a thermoerosional niche into a frozen bluff due to a storm surge on the Beaufort Sea coast. As a first attempt, the problem is treated as a one‐dimensional unsteady problem in which the vertical melting front of the thermoerosional niche migrates into the frozen bluff under the thermoerosional action of breaking waves inside the surf zone during a storm. The analysis examines the temporal and shore‐normal variations of the temperature and salinity of the seawater and the concentration of suspended sediment resulting from the migration of the melting front into the frozen bluff. A simple analytical solution is obtained for the case where the mean water depth during a storm is approximately constant in the neighborhood of the frozen bluff. An example computation based on the simple analytical solution indicates that the thermal driving of the ambient seawater, the mechanical driving represented by the water depth, and the duration of the storm surge are important in determining the degree of the thermoerosional niche formation into the frozen bluff. The computed results are also shown to be in qualitative agreement with available field observations.
Marine liquid aerosol production from bursting of air bubbles
Authors: Resch F. J. , Darrozes J. S. , Afeti G. M.
Published: February 2008

The action of wind stress upon the marine surface is responsible for producing air bubbles in seawater through wave breaking. After a given residence time in the sea, bubbles return to the surface, where they burst. The phenomenon of bursting produces two families of droplets: film drops and jet drops. The characteristics of jet drops are far better known than those of film drops. By means of an in‐line holographic technique one can obtain experimental results through visualization. One can observe the successive stages of the bursting process of a single bubble in deionized fresh water and in seawater. One visualizes both film drops and jet drops generated by bubbles whose diameter may attain 10 mm. The onset of the bursting phenomenon is clearly shown. Film drop count and size are measurable and may be compared with other available estimates.
A model of gas transfer across air‐water interfaces with capillary waves
Authors: Coantic Michel
Published: February 2008

The transfer of weakly soluble gases between the atmosphere and seas or lakes is controlled by liquid‐phase molecular and turbulent diffusion mechanisms, which essentially depend on wind velocity and gas Schmidt number. A distinct change in regime is observed around 2–3 m s−1, when capillary waves appear, which present models cannot explain. We suggest relating turbulent diffusivity with (1) possible motions close to a “free” liquid‐gas interface, (2) mean current distribution in that region, and (3) capillary wave spectra. Resulting transfer velocities explain laboratory and field data at low and moderate wind speeds.
Determining the general circulation of the ocean: A nonlinear inverse problem
Authors: Mercier Herlé
Published: February 2008

The usual inversion procedures for determining the oceanic circulation take the density field as given. This does not explicitly account for the mismatch between the data, which are typically a single realization of the density field, and the circulation being estimated, which may be a time mean or some other smoothed quantity, but explicit consideration of the uncertainty of the density data renders the problem nonlinear, and new estimation methods have to be used. As an example, a nonlinear inversion is successfully applied here to the simple analytical model of Stommel and Veronis (1981). It is also shown that their linear procedure, if properly used, yields a much better result than they obtained.
Modeling of storm surges in the Bering Sea and Norton Sound
Authors: Johnson Walter R. , Kowalik Zygmunt
Published: February 2008

Sea level, currents, and ice distribution are studied in the Bering Sea during storm events. The ice and ice edge are incorporated into storm surge model. The interaction of wind, ice, and water is expressed by the normal and tangential stresses. A numerical grid is established for the Bering Sea, and a second refined grid is constructed for Norton Sound. Construction of open boundary conditions for the water and ice motion and numerical questions related to the application of a large frictional coefficient for ice are also discussed. Storm events from February and March 1982 are analyzed and compared with observations of bottom pressure and ice motion made by NOAA Pacific Marine Environmental Laboratory in the Bering Sea and sea level observations at Stebbins, Alaska. The influence of the ice on the storm surge propagation is shown, particularly that of the fast ice in Norton Sound. The model reproduces several observed features of the ice distribution in the Bering Sea, including the “race track” region off Nome, the polynya south of Saint Lawrence Island, and the movement of the ice edge.
The 1982–1983 El Niño signal off northern California
Authors: Rienecker Michele M. , Mooers Christopher N. K.
Published: February 2008

The major El Niño event of 1982–1983 affected the entire California Current system. The anomalous conditions along the west coast of North America were related to the equatorial anomalies and also to the anomalous atmospheric circulation in the northeast Pacific, where the Aleutian Low was east of its usual position and the associated 700‐mbar height reached its lowest value on record in February–March 1983. Positive temperature and negative salinity anomalies in the upper ocean, extending from the coast to at least 200 km offshore, were reported from San Diego to Vancouver Island. In data acquired in domains centered approximately 180 km off northern California by the Ocean Prediction Through Observation, Modeling and Analysis Program, anomalies in both temperature and salinity were most pronounced subsurface. Spatially and monthly averaged temperatures were about 3°C warmer than normal at 80 to 100 m in April and again in December 1983. At 100 to 120 m, salinity was about 0.4 parts per thousand lower than normal in July 1983 and July 1984, several months later than the temperature anomaly maxima. The temperature anomalies may be related to the poleward propagation of the equatorial El Niño perturbation by coastally trapped waves, with offshore propagation by planetary Rossby waves possibly playing some role in the relaxation of the perturbed eastern boundary current circulation. Anomalous onshore advection associated with the perturbed atmospheric circulation, deeper than normal mixed layers, or depression of the thermocline and halocline by the passage of Rossby waves could each account for coincident positive temperature and negative salinity anomalies.
Variation of the drag coefficient and its dependence on sea state
Authors: Geernaert Gerald L. , Katsaros Kristina B. , Richter Karl
Published: February 2008

Using a Gill propeller vane anemometer and resistance wave wires over a water column depth of 15 m, simultaneous measurements of the momentum flux and sea surface wave spectra were acquired from the Pisa mast, 28 km offshore in the German Bight during autumn and winter 1979. These data were analyzed to identify the relationship between wind stress and surface waves. It was found that wind stresses for wind speeds above 15 m/s were regularly higher than open ocean wind stresses as reported by Smith (1980) and by Large and Pond (1981) for the same mean wind speed. These results, when described in terms of the drag coefficient, compared closely with the results of Sheppard et al. (1972), who collected surface layer statistics over Lough Neagh, Northern Ireland. After modeling the surface waves of the North Sea as a function of wave saturation (or wave age), it became evident that variations in the magnitude of the drag coefficient could be explained by coincident variations in the surface wave energy spectrum. By applying the wave dependent roughness length model described by Kitaigorodskii (1973), the North Sea drag coefficient was predicted to be larger than drag coefficients reported from the open sea.
Circulation and nutrients in middepth Atlantic waters
Authors: Kawase Mitsuhiro , Sarmiento Jorge L.
Published: February 2008

Isopycnal analyses of distributions of salinity, oxygen, apparent oxygen utilization, nitrate, and silica in the depth range 800–3000 m in the North and Tropical Atlantic Ocean are carried out using data from the Transient Tracers in the Oceans, Meteor cruise 56 leg 5, Atlantis II cruise 109 legs 1 and 3, and the GEOSECS Atlantic Study. The results are summarized in isopycnal distribution maps and property‐property plots. The layer between 800 and 1500 m is oxygen poor and nutrient rich and is poorly ventilated. Below this is a better aerated layer with the deep western boundary current, part of which separates along the equator. Regeneration of nutrients and consumption of oxygen persist into the deep ocean in regions off the west coast of Africa. The Mediterranean Outflow Water apparently is causing significant cross‐isopycnal mixing through salt fingering. The resultant cross‐isopycnal velocity may be large enough to cause significant vorticity stretching.
Horizontal mixing in the Atlantic Equatorial Undercurrent estimated from drifting buoy clusters
Authors: Fahrbach E. , Brockmann C. , Meincke J.
Published: February 2008

During 1978 and 1979, four experiments with clusters of 6 to 10 drifting buoys were carried out in the Atlantic Equatorial Undercurrent. The measurements were intended to estimate horizontal mixing and its possible contribution to the salt loss of the high‐salinity core related to the Equatorial Undercurrent. The buoys were drogued at the estimated depth of the salinity core of 70 m to 90 m. The diameters of the spreading clusters ranged from 3 to 10 km. Each experiment was maintained for about 2 days. During this period the buoys were tracked by radar from a nearby operating research vessel. From the observed tracks, horizontal turbulent mixing coefficients were deduced. The results show a dependence on the horizontal scale of l1.43. This is not significantly different from an expected l4/3 law. Using the obtained scale dependence, the observations are extrapolated to the scale of the salinity core of 150 km obtained from hydrographic observations, resulting in a turbulent mixing coefficient of 6.5 × 106 cm2 s−1. Combining these numbers with the horizontal gradients of the salinity core, one obtains a salt loss of 1.42 g s−1 cm−1, which amounts to 20% of the complete salt loss of 7.2 g s−1 cm−1 compiled by Katz et al. (1980).
A maximum‐gradient inverse for the Gulf Stream system
Authors: Cornuelle Bruce D. , Malanotte‐Rizzoli Paola
Published: February 2008

Acoustic tomography uses integrating measurements which require inverse methods to resolve the averages into estimates of spatial structure. Statistical inverse methods have been extensively used to solve the reconstruction problem over different tomographic ranges and configurations. These inverses become very difficult to apply in frontal regions like the Gulf Stream (GS) system, where the statistics are acutely inhomogeneous and anisotropic and the mean is not a likely representation of the GS front at any time. In this paper we propose an alternative inverse which asks for the solution which gives a front instead of asking for the smoothest solution. The inverse solution minimizes the errors in the fit to the data while simultaneously maximizing the sum of the squares of the gradients observed in the reconstructed section and minimizing the absolute value norm for stability. The inverse is aimed at detecting changes in the GS front, thus the data are used to estimate the perturbations to a previous estimate of the frontal structure, instead of reconstructing the entire front as a perturbation from some average state. This approach is intended to merge well with eventual dynamic updating schemes and can be used with various types of data, given a proper model. Several examples have been run intercomparing the traditional linear least squares (LLSI) with the maximum gradient inverse (MGI), from very idealized cases to a real Gulf Stream section reconstructed from hydrographic data. Different transceiver configurations were also compared and mid‐depth instruments were found to be superior to bottom mounted instruments. The simplest cases show a significant improvement in the estimate of the Gulf Stream front by the MGI compared to the weighted least squares inverse (LLSI). As the cases became more complicated (and more realistic), the differences between inverse methods become less pronounced, although the strength and location of the perturbation maxima were always determined more accurately by the MGI. The decline is at least partially due to the numerical algorithm which lumps data misfits and external constraints (the maximum gradient) into a single penalty criterion which is minimized. The most immediate way to overcome this limitation is to break up the problem into a two‐step procedure, first a least squares inverse to fit the data and second an iterative, nonlinear optimization maximizing the gradient and minimizing the absolute value norm.
Mean surface energy fluxes over the global ocean
Authors: Hsiung Jane
Published: February 2008

A newly available consolidated data set from the U.S. Navy's Fleet Numerical Weather Central in Monterey, California, is utilized to investigate global energy fluxes at the sea‐air interface. Sea surface temperature data from January 1949 to December 1979 were extracted from the data set along with air temperature, sea level pressure, dew point temperature, wind speed, wind direction, and cloud cover. Five degree latitude by five degree longitude spatial averaging and monthly temporal averaging were applied to the parameters in the data set for the purpose of studying long‐term large‐scale fluctuations. The heat balance of the global ocean surface layer is calculated using bulk flux formulations. Maps of the long‐term monthly and annual means of the net surface energy flux together with the four components of the total flux (latent heat flux, sensible heat flux, incoming radiation, and outgoing radiation) for the global oceans are presented. Incoming solar radiation and latent heat flux are the two dominant components that control net surface energy fluxes. Wind speed, cloud cover, and the gradient of specific humidity are the three most important meteorological parameters in determining surface flux. Errors associated with the bulk formula calculations and the significant features of the energy balance at the ocean surface are discussed.
Large‐scale short‐period sea ice atmosphere interaction
Authors: Cahalan Robert F. , Chiu Long S.
Published: February 2008

Changes in the microwave brightness temperature measured by the Electrically Scanning Microwave Radiometer (ESMR) flown on board the Nimbus V satellite reveal large‐scale sea ice fluctuations in the Antarctic marginal ice zone. These ice margin fluctuations are predominantly wave numbers 1–4, with phase speeds of about 3 m/s independent of wave number. The spatial pattern and eastward advection of the sea ice anomalies match those of the atmospheric sea level pressure, and are consistent with sea ice displacement due to surface wind stress. Examination of the outgoing longwave radiation indicates that suppression of high clouds in regions of increased sea ice increases the radiative cooling which contributes to maintaining the ice. Data from three winter seasons indicate about a one‐third probability of occurence of this large scale high frequency sea ice atmosphere interaction during any given 2‐week period in winter.
An investigation of the circulation of the Gulf of Mexico
Authors: Hofmann Eileen E. , Worley Steven J.
Published: February 2008

Empirical search and inverse techniques were used to reanalyze historical hydrographic data obtained in the Gulf of Mexico, February 12 to March 31, 1962. From these data, eight transects, which provide basin‐wide coverage of the gulf, were constructed. On the basis of water properties the circulation of the Gulf of Mexico was characterized as a three‐layer, mass‐conservative system. Along most sections an empirical search in density coordinates was sufficient to obtain an optimum reference level that balanced the transport in the three layers. An inverse correction was necessary to obtain a mass balance for those sections that crossed the Loop Current and mesoscale eddies. The density of the optimum reference level (σ1 = 32.17) obtained from this analysis corresponds approximately to the bottom of the Antarctic Intermediate Water layer that exists in the Gulf of Mexico. By using this optimum reference level, total velocity profiles at specific locations in the Gulf of Mexico were obtained. Taken together, these yielded a description of the winter circulation of this region. In general, the large‐scale circulation consists of a clockwise (anticyclonic) gyre which is most prominent in the upper 500 m. Eastward and westward transports associated with the gyre are approximately equal at about 5 × 106 m3 s−1. Variations to this flow are provided by the Loop Current in the eastern gulf and a cyclonic eddy in the northwestern gulf. Transports obtained for these circulation features are approximately 30 × 106 and 8 × 106 m3 s−1, respectively, which are in agreement with values obtained from other hydrographic surveys in the Gulf of Mexico.
Wind‐forced changes in Labrador Current transport
Authors: Thompson Keith R. , Lazier John R. N. , Taylor Barbara
Published: February 2008

Three years of current data from the offshore branch of the Labrador Current are examined. The meters were at least 400 m deep (to avoid being struck by icebergs) and positioned over the 1000‐m isobath on the eastern flank of Hamilton Bank. The currents are predominantly directed along isobath. At periods of 1–8 days the motion is bottom‐intensified; at longer periods (10–40 days) it is essentially independent of depth. One of the objectives of this paper is to determine whether or not the 10‐ to 40‐day fluctuations, which are O(5 cm s−1), can be explained by large‐scale wind forcing over the North Atlantic. Monthly variations in the transport of the North Atlantic are calculated by means of the topographic Sverdrup relationship. The Sverdrup return flow along the coast of Labrador, −〈ψw〉, is found to have a well‐defined seasonal cycle with a range of 6 Sv. The maximum southward transport generally occurs in February, which is also the month when the standard deviation of (ψw) is a maximum (9 Sv). If we assume that the monthly changes of the return flow are barotropic and confined to a boundary current of (say) 100 km width and 1 km depth (the mooring depth), then 1 Sv corresponds to a speed of 1 cm s−1. We would then expect the large‐scale wind over the North Atlantic to cause the flow along the Labrador coast to vary with a seasonal range of 6 cm s−1 and exhibit monthly variations in winter of ∼9 cm s−1. However, a comparison of the (ψw) and current records shows no similarity. We therefore speculate, with some corroborative evidence from an analysis of Nain sea level, that these energetic variations in the (topographic) Sverdrup return flow along the Labrador Coast probably occur in deeper water, offshore of the current meter mooring. The cause of the barotropic current variations remains unclear. It is possible that they do not reflect genuine transport changes but are due to a meandering of the Labrador Current. Further analysis, and perhaps measurements of bottom pressure, are required to explore this possibility.
Water stress and ocean current measurements under first‐year sea ice in the Canadian Arctic
Authors: Shirasawa Kunio
Published: February 2008

Ocean current profiles were measured to calculate the ice‐water drag coefficent for tidal currents under landfast ice at the intersection of Lancaster Sound and Navy Board Inlet in the Canadian Arctic. Under‐ice current profiles showed 1–3 m of a logarithmic layer with a friction velocity ranging from 0.3 to 1.0 cm/s. No significant Ekman veering was found below the logarithmic layer, which suggests a strong modulation of the surface current by tidal currents. The ice‐water drag coefficients at 1‐m depth, calculated from the mean current profiles, ranged from 0.0053 to 0.0093, reflecting a nonhomogeneous rough surface and ridges. It was shown that the present estimate of the drag coefficient was consistent with previously measured values of the ice stress.
Behavior of 226Ra in the Mississippi River mixing zone
Authors: Moore Daniel G. , Scott Martha R.
Published: February 2008

The behavior of 226Ra in the Mississippi River mixing zone is strongly nonconservative and includes desorption similar to that reported for the Hudson, Pee Dee, and Amazon rivers. However, dissolved and desorbed 226Ra concentrations in the Mississippi are 2 to 5 times greater than in the other rivers at the same salinity. Radium concentrations vary inversely with the water discharge rate. The 226Ra desorption maximum occurs at a salinity of 5.0, much lower than the 18 to 28 salinity values for the maxima of the other three rivers. High concentrations of dissolved 226Ra (up to 82 dpm per 100 L) and the low salinity values for the desorption maximum in the Mississippi River result from three major factors. Suspended sediments include a large fraction of montmorillonite, which gives the sediment a high cation exchange capacity, 0.54 meq/g. The average suspended sediment load is large, about 510 mg/L, and contains 1.9 dpm/g desorbable 226Ra. The dissolved 226Ra river water end‐member (9.6 dpm per 100 L) is higher than in surface seawater. The annual contribution of 226Ra to the ocean from the Mississippi River is 3.7 × 1014 dpm/yr, based on data from three cruises. Evidence of flux of 226Ra from estuarine and shelf sediments is common in vertical profile sampling of the deltaic waters but is not reflected in calculations made with an “apparent” river water Ra value extrapolated to zero salinity.
Deep‐sea currents off northern California
Authors: Stabeno Phyllis J. , Smith Robert L.
Published: February 2008

Current meter records from 14 moorings in the deep‐sea basin (3000–4500 m deep) south of the Mendocino Fracture Zone are analyzed. All moorings had current meters between 200 m and 500 m above the bottom, and some extended to within 150 m of the surface. There were high vertical correlations between measurements on the same mooring within 1500 m of the bottom and within 800 m of the surface but almost no significant correlation in the horizontal. In the basin the presence of eddies appears strongest at depths below 1200 m. Several of the records exceed 3 years in length, and one extended for 5 years. Spectral analysis of these shows that most of the kinetic energy below 3000 m is in the temporal mesoscale (periods of 31 to 120 days), while the spectral estimates in the upper 1000 m are dominated by longer time scales. Only in the deep records is there a significant southward mean flow. Neither a mean California Current nor a poleward undercurrent is apparent in the shallower data (above 1250 m). The currents in the upper 500 m nearest the continental margin are influenced by the presence of cold filaments originating near Point Arena.
Observations of internal gravity waves under the Arctic pack ice
Authors: Levine Murray D. , Paulson Clayton A. , Morison James H.
Published: February 2008

Internal gravity waves measured under the Arctic pack ice were strikingly different from measurements at lower latitudes. The total wave energy, integrated over the internal wave frequency band, was lower by a factor of 0.03–0.07, and the spectral slope at high frequency was nearly −1 in contrast to the − 2 observed at lower latitudes. This result has implications for theoretical investigations of the generation, evolution, and destruction of internal waves and is also important for other processes, such as the propagation of sound, and the wave‐induced turbulent diffusion of heat, plankton, and chemical tracers.
Large‐scale response to atmospheric forcing of shelf currents and coastal sea level off the west coast of North America: May‐July 1981 and 1982
Authors: Denbo D. W. , Allen J. S.
Published: February 2008

The response of alongshore currents V over the continental shelf and of coastal sea level ζ along the Pacific coast of North America to atmospheric forcing on large alongshore scales (100–2000 km) during May‐July 1981 (Coastal Ocean Dynamics Experiment (CODE) 1) and May‐July 1982 (CODE 2) has been studied using sea level and wind measurements from coastal stations and buoys between 33°N and 48°N and using current measurements from five locations between 35°N and 48°N. Characteristics of the large scale response of V and ζ to fluctuations in the alongshore component of the wind stress τ varied with latitude and with year in relation to variations in τ. In 1981, large‐scale ζ fluctuations were coherent within, but not between, separate domains north and south of 42°N. In 1982, large‐scale coherent fluctuations were found only in a northern domain that extended much farther south to near 37°N. Accordingly, in 1981, alongshore current V fluctuations from 39°N (CODE) were coherent with V from 35°N, while in 1982, V fluctuations from 39°N were coherent with those north to 48°N. In 1981 the northern domain fluctuations were forced by τ between 42°N and 45°N with southern domain forcing at 35°–36°N. In 1982, northern domain fluctuations were forced by τ over a region of much larger along‐shore extent (37°–48°N). High values of space‐lagged coherences between V and τ(y) (y is the alongshore coordinate) indicate that V at 39°N was strongly wind driven. Maximum squared coherences of V versus τ(y) are found with τ to the south by 100–300 km for low frequencies (ω ≤ 0.23 cpd in 1981, ω ≤ 0.14 cpd in 1982) and with τ from near‐local stations at higher ω, indicating the importance of remote forcing at low frequencies and local forcing at high frequencies. The response of V to τ(y) at 35°N and 43°N was more complicated, but evidence for strong wind forcing is found in several frequency bands for V at 43°N during 1981 and 1982 and at 35°N during 1981. At 48°N, V was forced in 1982 for ω ≤ 0.18 cpd by τ from locations 300–1400 km to the south.
Storm‐dominated bottom boundary layer dynamics on the Northern California Continental Shelf: Measurements and predictions
Authors: Cacchione David A. , Grant William D. , Drake David E. , Glenn Scott M.
Published: February 2008

Measurements of near‐bottom velocity profiles in 85 m water depth during a storm on the continental shelf off northern California using the GEOPROBE tripod in December 1979 provided estimates of shear velocities, u*, and roughness lengths, Z0, when the near‐bottom velocity profiles were logarithmic. These estimates agree within 90% confidence intervals with values computed from a simple near‐bottom combined wave‐current model that includes movable bed effects. The reasonably good comparison between model and profile estimates of u* suggests that such models can be used to predict bed shear stresses (or shear velocities) under combined flows of waves and currents typical of stormy conditions on continental shelves if stratification corrections to the velocity profile resulting from suspended sediment are small. The repeated occurrences of storms of similar intensities and wind velocities during the winter months off northern California suggest that the resultant high bottom stresses due to the combined effects of waves and currents are major factors in controlling the distribution of surficial sediment on the central portion of the northern California shelf.
Nutrient fluxes during extended blooms of Arctic ice algae
Authors: Cota G. F. , Prinsenberg S. J. , Bennett E. B. , Loder J. W. , Lewis M. R. , Anning J. L. , Watson N. H. F. , Harris L. R.
Published: February 2008

Estimates of nutrient demand by dense mats of ice algae in the high Arctic indicate that substantial nutrient fluxes are necessary to satisfy the observed growth over the 2‐month bloom. In our study area, Barrow Strait, the quantity of nutrients in the surface‐mixed layer is about 3–10 times greater than estimates of total demand during the bloom, and nutrient fluxes in the water column are estimated to be of the same order of magnitude as algal demand. The fluxes in the water column are predicted to vary by more than an order of magnitude over the fortnightly tidal cycle, assuming that fluxes depend upon the strength of tidal currents and the vertical nutrient gradients. In the latter half of the bloom, when biomass levels are high, it appears that established populations of ice algae may experience cyclic conditions of nutrient limitation during neap tides when nutrient fluxes are minimal. Contributions from regeneration and brine exclusion from the ice sheet appear to satisfy only a portion of the bloom's total requirement for nutrients.
Measurements of near‐surface shear in the ocean
Authors: Richman J. G. , de Szoeke R. A. , Davis R. E.
Published: February 2008

In an effort to measure current shear very near the sea surface a string of vector‐measuring current meters suspended beneath a surface float was deployed 180 km off southern California at 34°N 121°30′W on November 26, 1981 and allowed to drift freely for over 6 days. This arrangement, which we call the current meter drifter (CMD), gave measurements at depths of 2.5, 5.5, 8.5, 11.5, 14.5, 25, and 63 m. During the first two days, when the winds were light (≃8 m/s) and variable in direction, a nearly uniform current shear was observed in the upper 15 m with a low‐frequency velocity difference of 5 cm/s between the instruments at 2.5 and 14.5 m. During the last four days, when the winds were brisk (> 12 m/s) and steady in direction from the NNW, a strong downwind shear of order 10−2 s−1 was observed in the upper 10 m with a velocity difference of ∼7 cm/s between the instruments at 2.5 and 8.5 m. During this same period the shear below 10 m was much smaller. The average currents during the CMD drift veer to the right of the wind stress with angular displacement increasing with depth. Time series of the velocity difference between 2.5 and 5.5 m compare very well with θ(t)u*κ−1 ln (5.5/2.5), where θ(t) is the wind direction vector (of unit magnitude), u* = (wind stress/ρ)½ is the friction velocity in water, and κ = 0.4 is von Karman's constant. On the other hand, a similar comparison of the velocity difference between 5.5 and 8.5 m to θ(t)u*κ−1In (8.5/5.5) is much poorer with observed velocity difference being much larger, possibly due to stable stratification effects. Possible errors in the measurements have been considered and estimated as less than the observed velocity differences. Near‐surface shears as large as the observed are very important in closing the momentum budget for the oceanic boundary layer.
Comparison of satellite‐derived sea surface temperatures with in situ skin measurements
Authors: Schluessel P. , Shin H.‐Y. , Emery W. J. , Grassl H.
Published: February 2008

Sea surface temperatures (SSTs), computed from sensor systems on the National Oceanographic and Atmospheric Administration (NOAA) polar‐orbiting satellites, are compared with surface skin temperatures (from an infrared radiometer mounted on a ship) and subsurface temperature measurements. Three split window retrieval methods using channels 4 and 5 of the NOAA 7 advanced very high resolution radiometer (AVHRR) sensor were investigated. These methods were (1) using AVHRR alone, (2) using AVHRR with atmospheric temperature and water vapor profiles from the TIROS operational vertical sounder (TOVS), and (3) using AVHRR and data from the high‐resolution infrared sounder (HIRS). TOVS sensors (including HIRS) are carried by the same satellite as the AVHRR and provide simultaneous corrections for the AVHRR‐based SST estimates. The importance of scan angle correction to define the correct atmospheric path is discussed, and the improvement of SST retrievals using sensor combinations is demonstrated with satellite versus ship skin temperature mean differences ranging from 0.55° to 0.73°C for AVHRR alone, from −0.39° to 0.71°C for AVHRR plus TOVS, and from 0.22° to 0.33°C for AVHRR plus HIRS. The improved SST accuracy by AVHRR plus HIRS is due to additional correction for the atmospheric water vapor and temperature structures, made possible with some of the HIRS channels. Significant differences between ship skin and subsurface temperatures were observed, with the mean deviation being 0.2°C for a range of temperature differences between −0.25° and 0.6°C.
Turbidity currents and submarine channel formation in Rupert Inlet, British Columbia: 1. Surge observations
Authors: Hay Alex E.
Published: February 2008

Acoustic backscatter images obtained at 107 and 200 kHz of surge‐type turbidity currents resulting from mine tailing discharge are presented. Excess densities in the head of the order of 100 kg m−3 are estimated from differences in acoustic backscatter intensity and in the amplitude of the bottom‐reflected signal. These excess densities are comparable to estimates based on surge height and speed, the speed being determined by assuming a universal head shape. Unlike gravity current surges from an impulsively started steady source, the surge‐type turbidity flows consist of a high concentration slug of short duration followed by a longer‐lived wake in which sediment concentrations are lower by 2–3 orders of magnitude. The profile of the high concentration slug resembles those for density slugs on small bottom slopes obtained in laboratory experiments. Discrete scatterers, probably fish, are observed to avoid the surges.
Ocean acoustic tomography: Mesoscale velocity
Authors: Howe Bruce M. , Worcester Peter F. , Spindel Robert C.
Published: February 2008

The travel times of acoustic pulses transmitted in opposite directions over a 300‐km distance in mid‐ocean have been used to measure the fields of sound speed and absolute water velocity with mesoscale resolution. The experiment, which took place west of Bermuda during August and September 1983, consisted of transceivers on two moorings that sent and received signals every 2 hours for 21 days. Ray paths in opposite directions were found to be very nearly reciprocal; effects due to internal waves and mean currents were small. Sum travel times were inverted to obtain sound speed at 2‐day intervals, and differential travel times were inverted to obtain absolute current velocity u. The principal results are (1) range‐averaged sound speed perturbation δC(z) decreased over the 21 days by 5 ±0.2 m s−1 at 1000m depth, corresponding to a temperature decrease of approximately 1°C; similar (but lesser) changes are measured at other depths. The changes are associated with the first baroclinic mode. (2) The field δC(x,z) determined from expendable bathythermograph (XBT) measurements at the start of the experiment agrees with the field determined using the acoustic data within estimated errors of ± 1.6 m s−1. It is thus possible to obtain range‐dependent δC information from acoustic measurements made in a single vertical slice. (3) During the 21 days the range‐averaged barotropic velocity mode increased by a factor of 3, while the baroclinic mode decreased by a factor of 2. The estimated error in range‐averaged u(z) is ±2 cm s−1 above the main thermocline and ±1 cm s−1 below, while for range‐dependent u (x,z) the errors are 5 and 3 cm s−1, respectively. No significant range dependence in u (x,z) was found. The baroclinic velocity agrees with geostrophic velocities inferred from the XBT measurements at deployment and aircraft‐deployed XBT measurements 11 days after the end of the reciprocal transmissions.
Water masses and currents of the Southern Ocean at the Greenwich Meridian
Authors: Whitworth Thomas , Nowlin Worth D.
Published: February 2008

The frontal structure of the Antarctic Circumpolar Current (ACC) at the Greenwich Meridian is similar to that at Drake Passage even though the current is not confined to flow between two continents: There are sharp horizontal gradients in all properties throughout the water column, the fronts are narrow relative to the total width of the current, and most of the transport occurs within the frontal zones. East of Drake Passage, saline North Atlantic Deep Water (NADW) is incorporated into the Circumpolar current, and at the Greenwich Meridian it influences the water characteristics as far south as the Polar Front. Although the transport between Antarctica and Africa is close to that between Antarctica and South America, the transport within the ACC at our section is about 20% greater than at Drake Passage, probably due in part to the addition of NADW. Separating the ACC from the Weddell Gyre is a sharp front, south of which the signature of all but the densest Circumpolar Deep Water (CDW) is lost by mixing with the surface waters. The intermediate water of the central Weddell Gyre is formed from this dense CDW, which is modified by biochemical processes to become oxygen poor and nutrient rich. Warm, salty, less dense CDW from the southern edge of the ACC rounds the eastern end of the gyre and appears in the southern limb, which meanders around Maud Rise.
Variations of mesoscale and large‐scale sea ice morphology in the 1984 Marginal Ice Zone Experiment as observed by microwave remote sensing
Authors: Campbell W. J. , Gloersen P. , Josberger E. G. , Johannessen O. M. , Guest P. S. , Mognard N. , Shuchman R. , Burns B. A. , Lannelongue N. , Davidson K. L.
Published: February 2008

During the summer 1984 Marginal Ice Zone Experiment in the Fram Strait and Greenland Sea (MIZEX '84), passive and active microwave sensors on five aircraft and the Nimbus 7 scanning multichannel microwave radiometer (SMMR) acquired synoptic sequential observations which when combined give a comprehensive sequential description of the mesoscale and large‐scale ice morphology variations during the period June 9 through July 16, 1984. The high‐resolution ice concentration distributions in these images agree well with the low‐resolution SMMR distributions. For diffuse ice edges the 30% SMMR ice concentration isopleth corresponds to the ice edge, while for compact conditions the ice edge falls within the 40 to 50% SMMR isopleths. Throughout the experiment, ice edge meanders and eddies repeatedly formed, moved, and disappeared, but the ice edge remained within a 100‐km‐wide zone. The ice pack behind this alternately diffuse and compact edge underwent rapid and pronounced variations in ice concentration over a 200‐km‐wide zone. The aircraft microwave images show the complex structures and ephemeral nature of the mesoscale sea ice morphology. The difference in oceanographic forcing between the eastern and western sectors of the experiment area generated pronounced ice morphology differences. On the Yermak Plateau, from 3°E to 10°E, the weak ocean circulation allowed the wind to be the dominant force in determining the ice morphology. To the southwest of this region, over the Molloy Deep and the Greenland continental shelf break, from 3°E to 8°W, the ice morphology was dominated by the energetic East Greenland Current with its associated eddies and meanders.
Mesoscale variations in surface stress, heat fluxes, and drag coefficient in the marginal ice zone during the 1983 Marginal Ice Zone Experiment
Authors: Fairall C. W. , Markson R.
Published: February 2008

A series of turbulence and mean meteorological measurements were made from an instrumented aircraft during the 1983 Marginal Ice Zone Experiment in the Greenland Sea in July 1983. Using the inertial‐dissipation method, estimates of the surface fluxes of momentum, sensible heat, and latent heat have been obtained for five transects across the marginal ice zone (MIZ). The total heat flux was found to be about 30 W m−2 over the ocean and near zero over the ice. The 10‐m neutral drag coefficient went from an average of 1.3 × 10−3 over the ocean to 3.3 × 10−3 over the pack ice (a total distance of about 160 km). Most of the change occurred in a region about 60 km wide. In “sea breeze” conditions the surface stress was reduced about a factor of 2 in the MIZ center by stability effects.
Formation processes of brine drainage channels in sea ice
Authors: Wakatsuchi Masaaki , Kawamura Toshiyuki
Published: February 2008

This paper is an experimental study of the crystallographic circumstances governing the formation of brine drainage channels in sea ice. The study shows that brine channels always form in the grain boundaries toward which the ice platelets grow from both sides and that they do not form at the boundaries from which the platelets slant away. These observations imply that brine expulsion and gravity drainage are the major contributors to sea ice desalination.
The interpretation of the Icelandic sea ice record
Authors: Kelly P. M. , Goodess C. M. , Cherry B. S. G.
Published: February 2008

The representativeness of the Icelandic sea ice record, one of the longest climate indicators for the North Atlantic sector, is assessed by statistical analysis. Correlation of the sea ice index with ice concentration data for the adjacent seas suggests that the index is a reasonable measure of the ice cover of a large area of the northern North Atlantic sector. Associations with surface air temperature and sea level pressure are strong but regional rather than hemispheric in scale. The immediate causes of the variable advance of ice onto the Icelandic coasts are clear in the analysis of the atmospheric circulation data. Severe ice conditions are associated with enhanced anticyclonicity in the Icelandic region and stronger northerly and westerly winds over the Greenland Sea. It is concluded that the Icelandic index is a useful indicator of the state of the atmospheric flow north of Iceland and of the character of the East Greenland Current, one of the major avenues of meridional heat exchange in the climate system.
Field evaluation of an electromagnetic current meter based vertical profiler
Authors: Hamblin P. F. , Marmoush Y. M. R. , Boyce F. M. , Smith A. A.
Published: February 2008

A current profiler consisting of a vertical array of three electromagnetic current meters has been evaluated through an intercomparison of the three sensors, with reference to nearby current and wave data and by comparison to recent laboratory performance tests (Aubrey and Trowbridge, 1985). Mean flow estimates are too uncertain and variable to allow bottom boundary layer shear stress to be estimated by the conventional logarithmic law method. As well as unexplained sudden shifts in the mean speed response, the comparison with vector‐averaged current meter data indicates possible long‐term reduction in response due to fouling of the sensors by biological growth. The directional response was less sensitive to fouling effects. The oscillatory response on one occasion after field deployment for 17 days indicates a reduction in response from 41 to 45% at a period of oscillation of 3 s in a combined steady and oscillatory flow field. This study demonstrates that despite careful laboratory calibration, electromagnetic current meters are not at present suitable for quantitative study of dynamics of sediment resuspension in near‐bottom shallow‐water environments.