The application of strontium and neodymium radiogenic isotopes to South Atlantic paleoceanography

The main focus of this thesis is the use of radiogenic isotope records from deep sea sediment cores to track changes in ocean circulation over the last glacial cycle. The studies described herein focus on cores from the southeast Atlantic Ocean, a region where studies of traditional paleoceanographic tracers have yielded conflicting results. Changes in ocean circulation have been postulated to play an important role in the glacial cycles of the Pleistocene Epoch. The addition of new tracers to paleoceanographic research will better constrain past modes of ocean circulation, and ultimately contribute to a more complete understanding of the Earth's climate system.;Neodymium isotopes are applied to the question of whether the flux of North Atlantic Deep Water to the Southern Ocean changed over the last glacial cycle. In the South Atlantic, neodymium isotopes are sensitive monitors of the relative proportions of North Atlantic Deep Water and re-circulated Indo-Pacific water. The neodymium isotopic composition of the South Atlantic, as preserved in the Fe-Mn oxide component of RC 11-83, a Southeast Atlantic core, is interpreted to show a much reduced flux of NADW to the South Atlantic during cold stages of the last glacial cycle.;The downcore detrital strontium isotope record of RC 11-83 is also explored. This record varies closely with the benthic and planktonic stable isotopic records from this core. The strontium isotope record is interpreted with respect to the modern distribution of strontium isotopes and clay minerals in surface sediments, and with respect to surface water characteristics and downcore stable isotope records. The evidence suggests that the strontium isotopic variability reported in Chapter Four is controlled by the variability of the Agulhas Current over the last glacial cycle. The Agulhas is an important link in global thermohaline circulation, and changes in its flux may have an important influence on the heat and salinity budgets of the Atlantic Ocean.;Chapter Five considers the role of soils in the modern carbon cycle. Bomb radiocarbon is used as a tracer of carbon in soils subject to different agricultural methods.