Undergraduate Honors Theses

Thesis Defended

Spring 2011

Document Type

Thesis

Department

Geological Sciences

Abstract

Interannual variations in thermocline hydrography of the eastern tropical Pacific are today dominated by the El Niño/Southern Oscillation (ENSO). Mixed layer thickness, thermocline depth, and sea surface temperatures all decrease under La Niña conditions. Changes in these parameters are responsible for oceanographic and climate anomalies that have far reaching effects. Understanding how water column stratification of the eastern tropical Pacific has changed over time can lend insight into the past dynamics of ENSO, yet this is a poorly constrained area of study. We present a record of upper water column stratification history during the Holocene, using core PC14 from the Soledad Basin, Baja California (25.2N, 112.7W). We use Mg/Ca differences between G. bulloides, and N. pachyderma (d.) to reconstruct changes in the vertical stratification. G. bulloides reflects the upper most surface conditions during peak spring upwelling. N. pachyderma (d.) favors conditions near the bottom of the thermocline consistent with previous studies that it follows the Deep Chlorophyll Maximum (DCM). We apply this multi‐species approach to test the hypothesis, based on G. bulloides Mg/Ca, that the early to middle Holocene was characterized by millennial‐scale oscillations in ENSO mean state. Understanding the behavior of ENSO over long timescales can provide a path to evaluating the potential of orbital and solar forcing of ENSO dynamics.

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