Geostrophic currents

In the open ocean, the major advective water motion is associated with the surfece-water geostrophic currents and meridional overturning circulation. These flow paths are shown in Figures 4.4b and 4.6. Advection is much fester than molecular diffusion and turbulence. This enables water masses to retain their original temperatures and salinities as they are advected away from their sites of formation. Slow turbulent mixing with adjacent water masses eventually alters this temperatme and salinity signal beyond... 

NADW flows south from its site of formation until it reaches the Southern Ocean where it joins up with AABW The water masses then flow eastward under the influence of the Westerlies. A branch heads off into the Indian Ocean and the rest enters the South Pacific. All along these flow paths, upward advection and turbulent mixing slowly return the water to the surface where the geostrophic currents eventually carry it back to the Atlantic Ocean. Because a major feature of the flow paths is transport across latitudes. 

The abyssal clays are composed primarily of clay-sized clay minerals, quartz, and feldspar transported to the siuface ocean by aeolian transport. Since the winds that pick up these terrigenous particles travel in latitudinal bands (i.e., the Trades, Westerlies, and Polar Easterlies), the clays can be transported out over the ocean. When the winds weaken, the particles fell to the sea siufece and eventually settle to the seafloor. Since the particles are small, they can take thousands of years to reach the seafloor. A minor fraction of the abyssal clays are of riverine origin, carried seaward by geostrophic currents. Despite slow sedimentation rates (millimeters per thousand years), clay minerals, feldspar, and quartz are the dominant particles composing the surface sediments of the abyssal plains that lie below the CCD. Since a sediment must contain at least 70% by mass lithogenous particles to be classified as an abyssal clay, lithogenous particles can still be the major particle type in a biogenous ooze. 

Geostrophic current The advection of water resulting from the balance between gravity, wind stress, and the Coriolis Effect. 

Gyres A set of four interlocking geostrophic currents that move water in each ocean basin. Northern hemisphere gyres move surface waters clockwise, while southern hemisphere gyres move water counterclockwise. 

In contrast to the ocean, no significant permanent vertical component of the wind stress curl exists at the surface of the Baltic Sea since it is located entirely in one climate belt, namely the west wind belt. This implies that no permanent divergence of the Ekman transport in the open Baltic Sea and subsequently no up- or downwelling and hence no permanent geostrophic currents can be excited by the wind in the open Baltic Sea. 

In the Baltic Sea, the offshore scale for the transition of topography from the coast to the plain areas of the basins is commonly much larger than the baroclinic Rossby radius. Therefore, CTW can be used to analyze the dispersion and modal structure of sea level variations and quasi-geostrophic currents trapped at the basin rim. Some basins do not have well established plains, therefore, in these basins, the eigenvalue problem must be solved for the whole basin diameter, for example, the Eastern Gotland Basin. The CTW structures of both coasts splice each other in the center of the basin. Hence, CTWs are an effective mechanism for the communication between the rim and the center of the corresponding (e.g., Gotland) basin. 

The estimates of the climatic mean annual parameters of the MRC in the sections normal to the northeastern coast of the Black Sea presented in [17] yielded a distance of its core from the shore about 40 km, a full width of the current (with respect to velocity values of 0.02 m s-1) of 75 km, a penetration depth of 275 m, a maximal geostrophic velocity of 0.31 ms-1, and a volume transport of 1.3 x 106 m3 s x. These estimates are of the same order of magnitude as shown in Fig. 4a within the velocity interval to 0.20 m s x. This allows us to suggest a certain geographical universality (self-similarity) of the MRC profile normal to the coast. 

Lynch-Stieglitz J., Curry W. B., and Slowey N. (1999a) A geostrophic transport estimate for the Florida Current from the oxygen isotope composition of benthic foraminifera. Paleoceanography 14, 360-373. 

It is illuminating to study the time evolution of a river plume as an initial value problem. It can be shown that the current pattern is governed by a geostrophically adjusted eddy confined to the buoyancy patch (near field) and a coastally trapped flow that develops in the wake of a Kelvin wave (far field). Behind the front of the first Kelvin wave mode, undercurrents are set up. Although the velocities of the flow forced by the momenrnm of the river mnoff are small enough to justify a linear treatment, there are important nonlinear effects owing to the advection of density, which limits the validity of the linear analytical models. In particular, the structure of the near field in front of the river mouth is dominated by the response to the buoyancy flux associated with the river discharge. 

---