Description: Recent measurements indicate the transatlantic extent of the Namib Col Current at depths of 1300-3000 m near Lat. 22 degrees S in the South Atlantic Ocean. This current forms a continuous circulation structure from the Namib Col on the Walvis Ridge to the western trough, though its characteristic change as deepwater with varying properties enters and leaves the current owing to a meridional flow component. Transport estimates from hydrographic sections on the Walvis Ridge and at 15 degrees W near the crest of the Mid-Atlantic Ridge indicate a strength of about 3 x 10(6) m(3) s(-1) The current is part of a larger-scale eastward Row at Lon. 25 degrees W; transport estimates across the salinity maximum core there show a similar strength. Associated with this high-salinity high-oxygen current is a basin-wide front in these properties of varying intensity (weaker in the east) marking the transition to deep water whose North Atlantic characteristics have been partly erased by mixing with Circumpolar Deep Water in the southwest South Atlantic. The water which finally crosses the Walvis Ridge is supplied both by the eastward flow of this (diluted) North Atlantic Deep Water and by a general southeastward interior flow from the northern Angola Basin. Evidence suggests that this deep water continues south in the eastern Cape Basin, leaving the South Atlantic near the African continent.

Description: Measurements in the mixing zone of the Elbe estuary were performed during three consecutive tidal cycles with three types of instruments—a moored tripod with velocity and temperature/conductivity/light attenuation sensors, a profiling sonde with similar sensors lowered from an anchored vessel, and instrumented moorings. Acoustic-travel-time sensors were used for velocity measurements. Spectral analysis of 12·8 min pieces of the obtained time series gives results that are consistent with isotropic turbulence for part of the frequency space. Temporal changes of turbulent kinetic energy are correlated with tidal current velocity. A retardation is found between changes in tidal current and turbulent energy. Not all shear stress terms are in similar phase with tidal flow. Mean gradients, Reynolds stress terms, and turbulent salt flux terms are combined to determine eddy viscosity and eddy diffusion coefficients.

Description: Widespread and sustained in situ ocean measurements are essential to an improved understanding of the state of the ocean and its role in global change. Merchant marine vessels can play a major role in ocean monitoring, yet apart from routine weather observations and upper-ocean temperature measurements, they constitute a vastly underutilized resource due to lack of suitable instrumentation. Examples of ways in which vessels can assist include profiling techniques of physical properties, chemical sampling via automated water samplers, optical techniques to measure various biological parameters, and ground truth measurements for remote sensing from orbiting and geostationary satellites. Further, ships can act as relays between subsurface instrumentation and satellite communication services. To take advantage of the opportunities that the maritime industry can provide, two steps must be taken. The first is to initiate an instrumentation development program with emphasis on techniques optimized for highly automated use onboard ships at 15-20-kt speeds. The second is to forge partnerships or links between academic and government laboratories and the maritime industry for the institution and maintenance of such monitoring programs. No doubt significant resources will be required, but in the long run the improved ability to monitor the state of ocean in situ will make the effort more than worthwhile.

Description: The inclination of oceanographic mooring lines due to current drag causes errors in time series observations of currents and temperatures. The prediction of this effect requires knowledge of the drag coefficients for the mooring components. Drag coefficients, known for simple geometric shapes such as spheres or cylinders, are commonly used for mooring response computations. Selected mooring components (buoyancy elements and instruments) were tested in a tow tank to determine their actual drag coefficients. Over the Reynolds Number range, typical of oceanic conditions, deviations of the drag coefficient up to 50% are found when compared with the appropriate simple geometric shape coefficients. A set of model moorings and model current profiles is used to determine the resulting changes in component depth level and displacement. The changes in horizontal displacement of the upper part of the mooring are on the order of 10% in extreme cases and 1% under typical conditions. Their effects on current measurements will usually be negligible. However, the related vertical displacements are on the order 100 to 10 m. Such vertical displacements may carry instruments to depth levels where currents and particularly thermocline temperatures are sufficiently different from the intended level to cause errors in the time series observations.

Description: Simulated transient-tracer distributions (tritium, 3H3, freons) on the isopycnal horizons σ0=26.5 and 26.8 kg m−3 are presented for the East Atlantic, 10° −40°N. Tracer transport is modeled by employing a baroclinic flow field based on empirical data in a kinematic isopycnal advection-diffusion numerical model, in which winter convection is taken as the mechanism of communication with the ocean surface layer, and the isopycnal diffusivity is a free parameter. Diapucnic transport is ignored. The simulations employ time-dependent tracer boundary conditions, which are constructed on the basis of available observations. Simulations are compared to data obtained on a meridional section in 1981 (F/S Meteor, cruise 56/5). Best simulations were obtained by means of a subjective optimization procedure. On both levels, the observed distributions and the best simulated distributions agree well. The fact that the surface boundary conditions and interior distributions of the tracers are distinctly different leads us to the conclusion that our model provides a consistent description of upper main-thermocline ventilation and interior transport Surface-water densities in February are found to represent adequately the winter outcrop boundaries with an uncertainty of about ±300 km across. The required isopycnal diffusivity south of 29°N is 1700 m2 s−1, and 2900 m2 s−1 further north (+70/−40%). Interior transport is found to be predominantly advective. Advective ventilation across 30.5°N east of 33°W amounts to only 12% and 40% for the 26.5 and 26.8 horizons of the total ventilation rates reported by Sarmiento. The North Atlantic/South Atlantic Central Water boundary near 15°N is found to be predominantly determined by advection.

Description: Quasi-homogeneous layers in vertical profiles of temperature and salinity in the eastern North Atlantic near Madeira indicate the existence of a subtropical Mode Water in the Eastern Basin. Temperature sections show a maximum horizontal extent of at least 500 km. The frequency distribution analysis of homogeneous layers in a historical XBT dataset shows a Mode Water formation region near and to the north of Madeira. This Mode Water is found at increasing depths and displaced to the west and southwest during the course of the year after its formation by wintertime convection. It disappears almost completely, due to mixing, before the next winter. Volume estimates suggest that this Madeira Mode Water in the eastern Atlantic accounts for 15–20% of the total Central Water formation in the corresponding density range as obtained from tracer studies in the North Atlantic gyre.

Description: In the western equatorial Pacific the low-salinity core of Antarctic Intermediate Water (AAIW) is found at about 800 m depth between potential density levels σθ = 27.2 and 27.3. The pathways of AAIW and the degradation of its core are studied, from the Bismarck Sea to the Caroline Basins and into the zonal equatorial current system. Both historical and new observational data, and results from numerical circulation model runs are used. The observations include hydrographic stations from German and Japanese research vessels, and Eulerian and Lagrangian current measurements. The model is the JAMSTEC high-resolution numerical model based on the Modular Ocean Model (MOM 2). The general agreement between results from the observations and from the model enables us to diagnose properties and to provide new information on the AAIW. The analysis confirms the paramount influence of topography on the spreading of the AAIW tongue north of New Guinea. Two cores of AAIW are found in the eastern Bismarck Sea. One core originates from Vitiaz Strait and one from St. George’s Channel, probably arriving on a cyclonic pathway. They merge in the western Bismarck Sea without much change in their total salt content, and the uniform core then increases considerably in salt content when subjected to mixing in the Caroline Basins. Hydrographic and moored current observations as well as model results show a distinct annual signal in salinity and velocity in the AAIW core off New Guinea. It appears to be related to the monsoonal change that is typically found in the near-surface waters in the region. Lagrangian data are used to investigate the structure of the deep New Guinea Coastal Undercurrent, the related cross-equatorial flow and eddy-structure, and the embedment in the zonal equatorial current system. Results from 17 neutrally buoyant RAFOS floats, ballasted to drift in the AAIW core layer, are compared with a numerical tracking experiment. In the model 73 particles are released at five-day intervals from Station J (2.5°N, 142°E), simulating currents at a moored time series station north of New Guinea. Observed and model track patterns are fairly consistent in space and season. Floats cross the equator preferably north of Cenderawasih Bay, with a maximum range in eddy-motion in this region north of New Guinea. The northward route at 135°E is also reflected in a low-salinity tongue reaching up to 3°N. At that longitude the floats seem to ignore the zonally aligned equatorial undercurrents. Farther to the east (139 145°E), however, the float observations are consistent with low-latitude bands of intermediate currents.

Description: After some brief comments on the measurement of temperature and electrical conductivity in oceanography, the measuring probes suitable for in situ measurements are reviewed. Then the method of measurement is described using an improved model of the so-called bathysonde. This makes possible a continuous recording of temperature, conductivity, and pressure with high accuracy in great depths. Measurements from the Skagerrak and from the Mediterranean are considered. Finally, problems are discussed which arise when evaluating electrical conductivity and temperature from in situ measurements.

Description: Observations of temperature and electrical conductivity by a recording in situ salinometer are discussed in respect oo the physical processes connected with the renewal of North Atlantic deep water. The measured fine structure of the layering suggests that the downward movement of cooled surface water is combined with horizontal mixing down to more than 1000 m depth. This is confirmed by the existence of water elements which have slightly different temperature and salinity. Curves of temperature, conductivity, and salinity and T-S diagrams are shown.