Initial Reports of the Deep Sea Drilling Project - Volume 72

This volume covers Leg 72 of the cruises of the Drilling Vessel Glomar Challenger. DSDP Legs 71 to 75 in the South Atlantic were designed to study the circulation and climatic consequences of the growth of a long meridional ocean. With only limited drilling time available, the drilling program had to concentrate on a few, crucial parts of this development. One factor in the choice of objectives was the availability of the hydraulic piston corer (HPC), which permitted the study of less-consolidated sediments on a fine scale. Among the more important topics were: 1) early restricted circulation in small isolated basins; 2) development of an asymmetric circulation between eastern and western basins as the ocean widened; 3) interaction with steepening zonal climatic gradients through the Late Cretaceous and Cenozoic; evolution of the present intermediate and deep water mass structure. The importance of the anomalously elevated parts of the South Atlantic was recognized at an early stage; and the Falkland Plateau, Rio Grande Rise, and Walvis Ridge attracted a high proportion of the sites. Critical objectives for paleoceanographic drilling in the Rio Grande Rise and Vema Channel region on Leg 72 include the identification of the following: 1) Time of initiation of AABW flow into the Brazil Basin and northwestern Atlantic. 2) Time of initial formation of northern sources of bottom water, perhaps due to deepening of Greenland-Scotland Ridge in the Paleogene. 3) Major pulses of AABW and NADW during the Neogene and Quaternary. 4) Effects of southern hemisphere and northern hemisphere glaciation upon the production of AAIW, NADW, and AABW. 5) Effects of critical tectonic "threshold events" upon deep thermohaline flow. Leg 72 departed from and returned to Santos, Brazil, and took place between February and April of 1980.