Caitlyn Sarno

Date of Award

Spring 2019

Document Type

Open Access Thesis

Department

Marine Science

First Advisor

Claudia Benitez-Nelson

Abstract

Over the past several millennia, Southern California has experienced episodic climate that have influenced the magnitude and composition of terrestrial and marine material that ultimately reaches ocean sediments. Here, we analyze elemental concentrations, stable isotopes, and n-alkane lipids as tracers of terrestrial and marine sources in drought, turbidite, and flood horizons from a well-dated sediment core in the Santa Barbara Basin (SBB) that spans the last 2,000 years. Stable isotopes (δ13C and δ15N), indicate that more terrestrial organic carbon (OC) input occurred during floods relative to non-event periods, while bulk C/N ratios remained relatively constant (~10). Long chain n-alkanes, (C27, C29, C31, C33), characteristic of terrestrially derived OC, dominated all sediment types, but were 4 times more abundant during floods. Although relatively small in contribution to total OC burial, macrophytes (C21, C23) and marine algae (C15, C17, C19) also contributed 4 and 3 times more to flood sediments compared to non-event sediments, respectively. Turbidites had three times as much algal and macrophyte n-alkanes and twice as much terrestrial n-alkanes relative to non-event sediment. Drought sediment, on the other hand, was distinguishable from non-event sediment only by higher δ15N signatures. Combined, our data indicate that 8% of the total OC buried over the past 2,000 years occurred during 11 flood events, with 10% of deep sediment OC burial derived from shelf remobilization during 6 turbidite events. Comparison with modern day flooding suggests the large OC burial in flood sediments came from megafloods. Overall, our work confirms that flood events transport and bury significant terrestrially derived OC on continental shelves.

Rights

© 2019, Caitlyn Sarno

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