A long history of equatorial deep-water upwelling in the Pacific Ocean

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doi: 10.1016/j.epsl.2017.03.016
Author(s): Zhang, Yi Ge; Pagani, Mark; Henderiks, Jorijntje; Ren, Haojia
Author Affiliation(s): Primary:
Texas A&M University, Department of Oceanography, College Station, TX, United States
Other:
Yale University, Department of Geology and Geophysics, United States
Uppsala University, Department of Earth Sciences, Sweden
National Taiwan University, Department of Geosciences, China
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, Vol.467, p.1-9. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Includes appendix. 75 refs.; illus., incl. sketch map
Summary: Cold, nutrient- and CO2-rich waters upwelling in the eastern equatorial Pacific (EEP) give rise to the Pacific cold tongue. Quasi-periodic subsidence of the thermocline and attenuation in wind strength expressed by El Niño conditions decrease upwelling rates, increase surface-water temperatures in the EEP, and lead to changes in regional climates both near and far from the equatorial Pacific. EEP surface waters have elevated CO2 concentrations during neutral (upwelling) or La Niña (strong upwelling) conditions. In contrast, approximate air-sea CO2 equilibrium characterizes El Niño events. One hypothesis proposes that changes in physical oceanography led to the establishment of a deep tropical thermocline and expanded mixed-layer prior to 3 million years ago. These effects are argued to have substantially reduced deep-water upwelling rates in the EEP and promoted a "permanent El Niño-like" climate state. For this study, we test this supposition by reconstructing EEP "excess CO2" and upwelling history for the past 6.5 million years using the alkenone-pCO2 methodology. Contrary to previous assertions, our results indicate that average temporal conditions in the EEP over the past ∼6.5 million years were characterized by substantial CO2 disequilibrium and high nutrient delivery to surface waters - characteristics that imply strong upwelling of deep waters. Upwelling appears most vigorous between ∼6.5 to 4.5 million years ago coinciding with high accumulation rates of biogenic material during the late Miocene-early Pliocene "biogenic bloom".
Year of Publication: 2017
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Algae; Alkenones; Biogenic processes; Carbon; Carbon cycle; Carbon dioxide; Cenozoic; Coccolithophoraceae; East Pacific; El Nino; Equatorial Pacific; Geochemical cycle; Isotopes; Ketones; La Nina; Leg 130; Leg 138; Lower Pliocene; Microfossils; Miocene; Neogene; North Pacific; Northeast Pacific; Northwest Pacific; ODP Site 806; ODP Site 850; Ocean Drilling Program; Ontong Java Plateau; Organic compounds; Pacific Ocean; Paleo-oceanography; Paleocurrents; Plantae; Pliocene; Productivity; Sea water; Stable isotopes; Tertiary; Thermocline; Upper Miocene; Upwelling; West Pacific
Coordinates: N001906 N001907 E1592142 E1592140
N011749 N011751 W1103116 W1103118
Record ID: 2017045988
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands