Thermohaline Mixing Research Articles

Thermohaline structure and mixing in the region of Prydz Bay, Antarctica

Temperature and salinity data, collected during successive summer expeditions to the region of Prydz Bay, Antarctica between 1981 and 1985, indicate that the mixing processes responsible for the thermohaline circulation are similar to those in the Weddell Sea. In particular, Circumpolar Deep Water intrudes over the continental shelf break, aided by periodic upwelling processes associated with the tides and continental shelf waves, and mixes with the colder Shelf Water associated with the formation of sea ice over the continental shelf. Mixing of these intrusive water masses is enhanced by shear, and the resultant cold and salty mixture, termed here Prydz Bay Bottom Water, flows westward and downslope under the influence of the Coriolis force and Antarctic coastal winds. Prydz Bay Bottom Water is insufficiently dense to reach abyssal depths, and probably interleaves with the Circumpolar Deep Water at intermediate depths. The mixing processes are likely to be responsible for active bottom water formation in Prydz Bay for most of the year, except perhaps in the summer months when the mixture is insufficiently dense to flow down the continental slope.

Carbon Abundance in Mass-Exchanging Binaries

The evolution of the carbon abundance at the surface of both components of a mass-exchanging (Algol-type) binary is examined (fig. 1). Distinction is made between case B and case AB (fig. 2) of mass transfer, in view of the different timescales involved. In the mass accreting component thermohaline mixing is adopted when matter with decreasing hydrogen abundance is deposited on the surface.It is shown that at the surface of the loser a very low C-abundance is present, while at the surface of the gainer different regimes occur. On the average the expected C-abundance on the gainer is clearly lower than the observed solar value, but far above the value at the surface of the loser. The variation in time during the mass-exchange process is compared to the values, derived from observation of several Algol-type systems.

Sedimentation on Antarctic Sea Floor: ABSTRACT

The most common sediment type cored on the continental shelf is relict diamicton. Sediments were deposited by grounded ice (basal tills) through lodgement processes or from floating ice. The seaward limit of basal tills is the shelf edge. Glacial marine sediments derived from floating ice are probably deposited near the grounding line of ice shelves. Several criteria distinguish basal tills from glacial marine sediments. Sedimentation on exposed Antarctic continental shelf is predominantly marine rather than glacial. Antarctica generally lacks a wave dominated coastal zone and the continental shelf is unusually deep (average 500 m). Therefore, waves and wind-generated currents have little influence on bottom sediments. Tidal and thermohaline currents are apparently too weak to erode the cohesive basal tills and glacial marine sediments. Mass-flow processes are the important factors in shelf sedimentation today. Turbidites, consisting of well sorted quartz sands, are widespread on the continental margin and abyssal floor. These sands are commonly interbedded with poorly sorted glacial marine sediments. Calcareous turbidites have also been cored in the Ross Sea. Laminated siliceous oozes, which are almo t devoid of ice-rafted debris, fill many shelf depressions. At the shelf edge and upper slope, geostrophic currents erode the bottom and transport sands by traction, while silts and clays are suspended and transported parallel to the slope. These currents are disrupted only in areas where shelf waters are sufficiently dense to displace and mix with circumpolar waters (thermohaline mixing). This mixed bottom water flows downslope at velocities of only a few centimeters per second, depositing laminated silts along the flow path. Ice-rafting diminishes sharply seaward of the present ice front, and ice-rafted debris comprises a minor component of slope and rise deposits. End_of_Article - Last_Page 890------------

An observation of the gulf stream surface front structure by ship, aircraft, and satellite

Observations of surface temperature and salinity along the western edge of the Gulf Stream were made from a ship while concurrent temperature observations were obtained by instrumented aircraft at six altitudes. The major feature along a five-kilometer line normal to the Stream's edge is a temperature gradient of about 0.75°C/kilometer within which are embedded two abrupt temperature increases of about 1.5°C. Temperature variations were compensated by salinity variations, yielding nearly constant density through the frontal zone; a sharp lateral current shear was associated with the thermohaline mixing region between the steps. The attenuation of surface temperature measured by the airborne radiometer was compared with a theoretical model. The analysis supports the view that a two-part correction technique is required: one part for bulk-skin temperature differences, and another for atmospheric attenuation of sea surface emission due to the mass and temperature of interfering gases. Electronic noise and scan geometry of the Nimbus II radiometer experiment prohibits any discussion of detailed oceanographic variability as seen from space, however, the gross features of the front are reproduced to a fair degree of accuracy.