Oceanic circulation remains one of the poorly understood elements of the global
climate system, despite its importance to planetary heat redistribution and carbon
cycling. The nature of deep-water formation and circulation in ancient oceans are even
more poorly constrained. In order to understand climate dynamics of past and future
climates we must have a better understanding of the role of deep-ocean circulation.
In this dissertation I investigated changes in intermediate- to deep-water
circulation in three different ocean basins during two different geologic eras. The first
study focused on the late Pleistocene (~25 ? 60 ka) California margin to investigate the
role of intermediate water circulation in abrupt climate fluctuations. The other two
studies investigated deep-water circulation during the Late Cretaceous (~70 ? 100 Ma)
greenhouse interval, to determine if deep waters formed in the southern Indian or
Atlantic basins.
The above studies employed neodymium isotopes preserved in biogenic apatite
(fish teeth and bones) and foraminiferal calcite to reconstruct the provenance of intermediate- to deep-water masses. Here I present data from two sites located at
intermediate depths on the late Pleistocene California margin as well as seven Deep Sea
Drilling Project and Ocean Drilling Program Cretaceous aged sites; four in the South
Atlantic Ocean, and three in the Indian Ocean.
The new Pleistocene data rule out changes in the source of intermediate waters to
the California margin, thus the recorded changes in seafloor oxygenation were caused by
changes in sea surface productivity. In the Cretaceous, the spread of deep waters formed
in the high-latitude South Atlantic was hindered by tectonic barriers until the mid
Campanian when the subduction of Rio Grande Rise allowed for the continuous flow of
deep waters from the Southern Ocean into the North Atlantic. The deep Cretaceous
Indian Ocean was filled with deep waters formed in the high-latitude Indian Ocean, until
being replaced with waters sourced in the Pacific from the late Cenomanian to early
Campanian before a return to southern Indian-sourced waters for the remainder of the
study interval.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-05-8023 |
| Date | 2010 May 1900 |
| Creators | Murphy, Daniel Patrick |
| Contributors | Thomas, Deborah J. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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