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Modal properties of Antarctic Intermediate Water (AAIW) are determined from bivariate distribution diagrams for two regions in the southeast Pacific and two regions in the South Atlantic. The volumetric potential temperature-salinity diagrams reveal distinct differences between the intermediate waters of the southeast Pacific and the South Atlantic. The intermediate waters of the, southeast Pacific are more homogeneous than their counterpart in the South Atlantic. The potential temperature and salinity properties of the large volume mode intermediate water in the southeast Pacific are identical to those of the coldest variety of McCartney's (1977) Subantarctic Mode Water (SAMW). It is evident from volumetrically weighted-average properties that the intermediate water of the South Atlantic is primarily colder (∼1°C), denser (∼0.1 mg cm−3) and oxygen poorer(O.5 ml l−1) than the intermediate water of the southeast Pacific. If it is assumed that no AAIW formation takes place in the South Atlantic out...

Some of the characteristics of intrusive finestructure observed in oceanic fronts suggest that salt fingering is active in the intrusions. An extension of Stern's 1967 study of the stability of a thermohaline front to intrusive finestructure driven by salt fingers is presented to investigate this hypothesis. Intrusions are found to grow due to the salt finger induced density fluxes even in the presence of small scale momentum dissipation. The presence of this dissipation defines a fastest growing mode for the disturbance which has physical characteristics not unlike those observed in oceanic fronts. The model results do not agree well with the laboratory studies of intrusions. For many fronts, the model requires initial perturbations in the front which can support salt fingers. Linear internal waves are investigated to determine if they can provide the initial perturbation. It is shown that, away from the equator, the interaction between internal waves and intrusions is weak because of a mismatch of time scales. Finally, growing intrusions are shown to flux heat, salt and density across fronts. The senses of these fluxes are to run down the lateral gradients of many oceanic fronts.

Continuous conductivity-temperature-depth-dissolved-oxygen (CTD) data are used to investigate the spatial distribution of fine and microstructure between the Azores and Flemish Cap. The CTD data are used to calculate a conductivity-microstructure Cox number. This indicator summarizes microstructure variance from the 0.08–2 m vertical wavelength range. The CTD data are also used to calculate the finestructure-temperature Cox number. Finally, the fine and microstructure data are combined to calculate lateral flux and flux divergence for the waters east of the Atlantic Current. The distribution of the conductivity Cox number indicates that vertical mixing is more intense above the base of the main thermocline (5°C isotherm) than below it, and that mixing is more prominent near the North Atlantic Current than farther east. Stations near the front indicate elevated conductivity Cox numbers associated with intrusive features. The hydrographic sections and the finestructure data reveal the presence of i...

The component of the FDRAKE-75 data obtained by the R/V Conrad in the western Scotia Sea reveals a definite sequence of thermohaline stratification zones encountered on passing from Antarctic to Sub-antarctic waters. A Polar Front Zone, displaying multiple temperature minima, separates the Antarctic Zone, characterized by a single intense T-min above 200 m, from the Subantarctic Zone with its nearly isohaline layer from 100 m to over 400 m. The Antarctic Zones of the Weddell and the Scotia Seas aye separated by a cold, relatively homogeneous zone situated in the southern Scotia Sea called the Weddell-Scotia Confluence. The boundaries of the Polar Front Zone are highly meandered and isolated eddies of Subantarctic water may occur within the zone. The main axis of the Antarctic Circumpolar Current apparently lies close to the Subantarctic boundary of the, Polar Front Zone, while a secondary axis is associated with the southern limit of the Polar Front Zone. Inspection of the Islas Orcadas and Melvi...

Antarctic Intermediate Water and Subantarctic Mode Water are studied by examining their modal density and modal salinity characteristics around Antarctic. The study focuses on 15 regions between 40 and 45°S. Circumpolar distributions for the cores of Antarctic Intermediate and Subantarctic Mode Water and potential temperature-salinity diagrams provide a detailed description of the water masses. The modal salinity and density change gradually across each of the three oceans, presumably due to the alteration of a single water mass. Large changes occur in the transition regions in the Drake Passage, south of Africa, and south of New Zealand. These large changes are due to the presence of distinctly different water masses. Thermohaline finestructure is associated with the water mass transitions. The finestructure intensity between the 27.10 and 27.40 σθ isopycnals is quantified. Although continuous temperature-depth data are not available for the entire region the study indicates that the most intense finestructure occurs in regions of large water mass contrast and decreases by an order of magnitude away from them. Increased vertical temperature gradient variances were observed near a 100-km diameter eddy south of New Zealand.

Data from 137 new hydrographic stations are used with older hydrographic data to construct horizontal charts of potential temperature at 4000 m and the depth of the 0°C potential temperature surface for the southwestern South Atlantic. The data are also used to construct seven potentials temperature sections and to calculate bottom water transport. From the horizontal charts it is inferred that the abyssal circulation in the Argentine Basin and its southward extension consists of several distinct gyres. The most intense abyssal circulation is in the western Argentine Basin. It is suggested that these bottom waters are renewed by northward flow through the East Falkland Channel from the Georgia Basin. The Georgia Basin provides the most direct conduit to the western Argentine Basin for the cold, fresh bottom waters found in the vicinity of the South Sandwich Trench. The horizontal charts also indicate a southward flow from the Argentine Basin into the Georgia Basin of warmer bottom waters through the East Falkland Channel. These waters are found along the southern flank of the Falkland Fracture Zone and the eastern flank of the Islas Orcadas Rise. The vertical potential temperature sections illustrate the baroclinic structure of the western boundary currents over the South Sandwich Trench and along the Argentine Continental Slope. The calculated northward transports for waters with potential temperatures less than 0°C are largest (18 x 106 m3 s−1) at the southern end of the South Sandwich Trench just north of the Weddell Sea. The transports decrease to 5 x 106 m3 s−1 at the northwestern end of the trench. The major flow of cold bottom water into the Argentine Basin appears to be through the Georgia Basin, with 1 to 3 x 106 m3 s−1 flowing through the Falkland Channels. A reference level is chosen in the Argentine Basin that is coincident with the depth of the 0°C potential temperature surface that on the average is 2000 m deeper than that proposed by DEFANT (Wissenschaftliche Ergebnisse der Deutschen Atlantischen Expedition auf dem Forschungs- und Vermessungsschiff “Meteor”, 1925–1927, 6 (2, 5), 191–260, 1941) and used by Wust (Wissenschaftliche Ergebnisse der Deutschen Atlantischen Expedition auf dem Forschungs- und Vermessungsschiff “Meteor”, 1925–1927, 6 (2, 6), 261–420, 1957). The calculated transports for the deep and abyssal boundary currents in the western Argentine Basin are small (2 x 106 m3 s−1), less than one-tenth that calculated bu Wust (1957) for the bottom waters.

Prepared for the National Science Foundation - Office of International Decade of Ocean Exploration under Grant OCE-78-22223.

Prepared for the National Science Foundation - Office of International Decade of Ocean Exploration under Grant OCE-78-22223.

Volumetric analysis is used to quantify the observed changes in the Circumpolar Deep Water (CDW) potential temperature/salinity relationship along the axis of the Antarctic Circumpolar Current. A marked increase occurs in the CDW potential temperatures and salinities in the South Atlantic. However, the vertical density distribution is not significantly affected: The volume of water in the deep water density class intervals remains virtually unchanged. Lateral mixing with the warmer and saltier North Atlantic Deep Waters (NADW) and the colder and fresher Antarctic deep waters appears responsible for this change. Temperature and salinity inversions have been observed on continuous salinity-temperature-depth soundings in much of the South Atlantic. This fine structure, presumably the signature of lateral mixing and not of internal wave origin, is particularly evident in the southwestern Argentine Basin, where 0.5°C temperature inversions with 50–200 m vertical scales are found at the depth of the NADW/CDW confluence, between 1500 and 2500 m. To quantify the intensity of the fine structure the temperature-gradient variance in the 32–256 m vertical wavelength band is calculated for data from the southwest Argentine Basin the Drake Passage, Scotia Sea, the central and eastern Atlantic, and the southwest Indian Ocean. The largest variance levels occur in the Argentine Basin, the smallest in the Drake Passage, while those in the central Atlantic are intermediate. The temperature-gradient variance data from the Argentine Basin are then used to estimate the lateral temperature flux in the NADW/CDW confluence with a statistical model developed by Joyce (1977). The calculated quantities are small; the lateral temperature flux is of the order of 4 × 10−4°C m s−1 and the lateral diffusivity of order 40 m2 s−1. The data are also used to calculate heat flux divergences. The close agreement between the heat flux divergence calculated from the temperature changes of the CDW core and the divergence calculated with the fine structure data suggest that lateral mixing accounts for the large-scale property changes observed in the CDW core.

Temperature and salinity data from a repeated salinity-temperature-depth station and temperature profiles from three expendable bathythermograph experiments are used to investigate both the spatial and the temporal characteristics of fine structure observed in the Antarctic Polar Front Zone. The fine structure was found to evolve considerably on time scales of 1 hour and less. From an experiment designed to elucidate the spatial scales of the fine structure, a marked anisotropy was revealed, suggesting that the temperature structures were elongated filaments aligned with the front. The data were also used to investigate the possibility that internal waves generate the observed fine structure. On the basis of the temperature-salinity correlation of the fine structure and the extremely large required vertical displacements the vertical motions of internal waves can be ruled out as the primary cause of the fine structure. Because the Antarctic Polar Front Zone is a region of high horizontal temperature and salinity gradients and because there is an observed increase at one-half inertial period in drop-lagged coherences, it is hypothesized that the low-frequency nearly horizontal internal wave motions are generating the observed fine structure. However, in the particular case where direct observations of the vertical motions of internal waves are available, assuming that the relationship between vertical and horizontal displacements prescribed by the Garrett and Munk (1975) model holds, horizontal displacements are also ruled out as the sole source of the observed fine structure, yielding neither enough total variance nor the expected spectral shape; thus much of the observed variability may be attributed to temperature fine structure of noninternal wave origin.