Eastern Tropical Pacific Climate And El Niño Variability During The Past Millennium
type: CreativeWork
description: The El Niño Southern Oscillation (ENSO) has been implicated in large-scale climate shifts of the past millennia, but paleoclimate records from the dynamically vital eastern equatorial Pacific Ocean (EEP) spanning the past millennium are sparse. This has limited our understanding of tropical Pacific dynamics, leaving questions regarding the source of ENSO variability unanswered. Here I seek to address some of these questions regarding relationship between ENSO and tropical Pacific mean state, and the relationship between the tropical Pacific and large-scale climate. Mean EEP sea surface temperature (SST) for the past millennium was reconstructed using Mg/Ca ratios in Globigerinoides ruber from a sub-centennially resolved sediment core collected near the Galápagos Islands. ENSO activity for the past ~1000 years was reconstructed using oxygen isotope ratios (δ18Oc) from individual G. ruber foraminifera from the same sediments. For the first time, a "Mid-Millennial Shift" is identified at ~1500 CE when the tropical Pacific switched from a "La Niña-like" mean state with a strong zonal SST gradient and dampened ENSO to an "El Niño-like" mean state with weak zonal gradient and amplified ENSO. The ~350-year periods preceding and following ~1500 CE represent fundamentally different ocean-atmosphere circulation states in terms of both tropical Pacific mean state and variability. The Mid-Millennial Shift coincided with the deepest Little Ice Age cooling and a southward shift of the Intertropical Convergence Zone. This research provides context to the ENSO modulations of the past millennium by extending the SST record back to ~2700 years before present. This record reveals a long-term cooling trend of -0.22 ℃/ky, similar to Northern Hemisphere temperature trends suggesting a common origin, likely insolation forcing. Warm SST, within error of modern, is observed during the peak Medieval Climate Anomaly (~900-1150 CE), contradicting the prevailing La Niña-like paradigm. Much of t…
abstract: The El Niño Southern Oscillation (ENSO) has been implicated in large-scale climate shifts of the past millennia, but paleoclimate records from the dynamically vital eastern equatorial Pacific Ocean (EEP) spanning the past millennium are sparse. This has limited our understanding of tropical Pacific dynamics, leaving questions regarding the source of ENSO variability unanswered. Here I seek to address some of these questions regarding relationship between ENSO and tropical Pacific mean state, and the relationship between the tropical Pacific and large-scale climate. Mean EEP sea surface temperature (SST) for the past millennium was reconstructed using Mg/Ca ratios in Globigerinoides ruber from a sub-centennially resolved sediment core collected near the Galápagos Islands. ENSO activity for the past ~1000 years was reconstructed using oxygen isotope ratios (δ18Oc) from individual G. ruber foraminifera from the same sediments. For the first time, a "Mid-Millennial Shift" is identified at ~1500 CE when the tropical Pacific switched from a "La Niña-like" mean state with a strong zonal SST gradient and dampened ENSO to an "El Niño-like" mean state with weak zonal gradient and amplified ENSO. The ~350-year periods preceding and following ~1500 CE represent fundamentally different ocean-atmosphere circulation states in terms of both tropical Pacific mean state and variability. The Mid-Millennial Shift coincided with the deepest Little Ice Age cooling and a southward shift of the Intertropical Convergence Zone. This research provides context to the ENSO modulations of the past millennium by extending the SST record back to ~2700 years before present. This record reveals a long-term cooling trend of -0.22 ℃/ky, similar to Northern Hemisphere temperature trends suggesting a common origin, likely insolation forcing. Warm SST, within error of modern, is observed during the peak Medieval Climate Anomaly (~900-1150 CE), contradicting the prevailing La Niña-like paradigm. Much of t…
author: Rustic, Gerald Thomas
keywords: Geology, Paleontology, eastern tropical pacific; ENSO; foraminifera; paleoceanography; Paleoclimate
date published: 2015-09-30T07:00:00Z
date modified: 2026-07-24T01:58:31Z
provider: City University of New York - Graduate Center
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: The Graduate School and University Center of The City University of New York