Deep ocean circulation and continental weathering regimes during climate transitions (last deglaciation and Eocene-Oligocene) using strontium, neodymium, and lead isotopes in sedimentary archives.

摘要

The global climate on earth is constantly changing and periodically the earth system crosses a climate threshold and enters a new climate state. The Eocene-Oligocene transition (EOT) ∼33.4 Ma ago and the last deglaciation ∼18 ka are two examples of major climate transitions. During the EOT the Antarctic cryosphere developed, there was global cooling of deep waters, and the carbonate compensation depth deepened. During the last deglaciation there was massive global ice meltback, a dramatic rise in atmospheric CO2, and a decline in atmospheric Delta14C. These two events are climatologically important since the former represents the first Cenozoic transition from a greenhouse to an icehouse world, while the later represents the end of the last glacial period.;Major climate change is frequently associated with readjustment of carbon sources and sinks. The ocean is a relatively large carbon sink that can exchange carbon with the atmosphere over geologically short time scales. Chemical weathering of continental silicate rocks also plays a key role in sequestering atmospheric carbon over geologically long time scale. Therefore, the interplay between physical and chemical continental weathering can have major implications for the long term carbon budget of the Earth.;In this dissertation I studied continental weathering regimes on Antarctica during the EOT and the role of carbon storage and circulation in the ocean during the last deglacial in order to improve our understanding of the relationship between climate, ocean circulation, and continental weathering. Radiogenic isotopes of Pb, and Nd were extracted from sedimentary archives such as Fe-Mn oxide coatings and fossil fish teeth to acquire meaningful information pertaining to weathering and ocean circulation readjustments. Pb isotopic data from this study confirm a change in the Antarctic weathering regime leading up to the EOT, which may have contributed to the drawdown of atmospheric CO2 and ice buildup on Antarctica. I also documented a rearrangement of intermediate water circulation in the Pacific using Nd isotopic data recovered from fossil fish teeth. The old carbon that was trapped in the Southern Ocean abyss by sea ice or ocean stratification during the last glaciations was transported by intermediate waters and ventilated to the atmosphere following meltback of the ice at the end of the last glaciation.