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The nature of deep-sea sediments is important for understanding the mechanisms of sediment delivery and deposition to the deep ocean. This study describes and analyzes the size distribution of fine-grained biogenic opal and inorganic bottom sediments in the biologically productive, active upwelling region of the Eastern Equatorial Pacific (EEP). Using the Coulter Multisizer II, samples of biogeneous silica, inorganic silt and clay grains are analyzed from various depths in the seabed through a 200 cm cored interval that spans the age range of 1-30 ky B.P. Downcore variation in grain sizes is inferred to record changes in regional paleocurrent variability as well as fine siliclastic and opal delivery to the site. Results show that biogenic silica, in the form of opal, coarsens the sediments. However, this effect is not exhibited in the Holocene. Decreased delivery of mineral aerosols is inferred to be a mechanism to enhance the fine grain fraction of the samples. In agreement with other studies, stable paleocurrents are thought to characterize the 15-30 ky B.P. period. Comparatively, the 1-15 ky B.P. interval shows a more variable flow regime and is attributed to short-term instabilities of deep-water masses. For the paleocurrent reconstruction over latter interval, an anti-correlation is observed with respect to deep-water currents in the North Atlantic suggesting a dynamic inter-play between the Atlantic and Pacific deep water masses in global ocean thermohaline circulation in the Late Quaternary.

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Pages: 65
Supervisors: Markus Kienast (Oceanography) / Paul Hill (Oceanography)