Vertical thermal gradient history in the eastern Equatorial Pacific during the early to middle Miocene; implications for the equatorial thermocline development

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doi: 10.1002/2016PA003058
Author(s): Matsui, Hiroki; Nishi, Hiroshi; Kuroyanagi, Azumi; Hayashi, Hiroki; Ikehara, Minoru; Takashima, Reishi
Author Affiliation(s): Primary:
Tohoku University, Institute of Geology and Paleontology, Sendai, Japan
Other:
Shimane University, Japan
Kochi University, Japan
Volume Title: Paleoceanography
Source: Paleoceanography, 32(7), p.729-743. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0883-8305 CODEN: POCGEP
Note: In English. 76 refs.; illus., incl. sketch map
Summary: Knowledge of the equatorial thermocline is essential for understanding climate changes in the tropical Pacific. Multispecies planktic foraminiferal analyses provide a way to examine temperature distributions and thus the structure of the thermocline. Although the secular thermocline development has been documented back to the late Miocene, the early to middle Miocene interval has rarely been examined. In addition, relationships with the dynamic Antarctic ice sheets remain unclear. Here we investigate the vertical thermal gradient in the upper water column at Integrated Ocean Drilling Program Site U1337 in the eastern equatorial Pacific (EEP) throughout the early to middle Miocene (23.1 to 11.7 Ma). The gradient increased over the Miocene Climatic Optimum, whereas it decreased during the East Antarctic Ice Sheet Expansion (EAIE). Comparison of the EEP record with its western equatorial Pacific (WEP) counterpart suggests that sea surface temperature was more stable in the WEP than in the EEP. We further estimated equatorial thermocline from two diagonal gradients between the EEP and the WEP: thermocline shoaled from 16.7 to 15.7 Ma and tilt weakened between 16.5 and 13.8 Ma. The onset of the "Monterey Excursion" and the reduced Antarctic ice sheet volume would have affected thermocline depth and tilt, respectively. Thermocline depth was likely much deeper compared to Pliocene-to-modern conditions. Furthermore, a 4-point-based distribution of isotherms (4DI index) was used as a metric of the evenness or unevenness of the isotherm distributions. The 4DI index considerably reduced at around the EAIE and other Mi-events, reflecting the evenly distributed isotherms under a more glaciated Antarctica. Abstract Copyright (2017), . American Geophysical Union. All Rights Reserved.
Year of Publication: 2017
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; C-13/C-12; Carbon; Cenozoic; Dentoglobigerina venezuelana; East Pacific; Equatorial Pacific; Expedition 321; Expeditions 320/321; Foraminifera; IODP Site U1337; Integrated Ocean Drilling Program; Invertebrates; Isotope ratios; Isotopes; Marine environment; Microfossils; Miocene; Neogene; North Pacific; Northeast Pacific; O-18/O-16; Oxygen; Pacific Ocean; Paleo-oceanography; Paleoenvironment; Paragloborotalia siakensis; Protists; Stable isotopes; Tertiary; Thermocline
Coordinates: N035000 N035000 W1231222 W1231222
Record ID: 2017085898
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom