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Climate of the Past An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/cp-2017-151
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
20 Nov 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).
Thermocline state change in the Eastern Equatorial Pacific during the late Pliocene/early Pleistocene intensification of Northern Hemisphere Glaciation
Kim A. Jakob1, Jörg Pross1, Christian Scholz1, Jens Fiebig2, and Oliver Friedrich1 1Institute of Earth Sciences, Heidelberg University, Heidelberg, 69120, Germany
2Institute of Geosciences, Goethe-University Frankfurt, Frankfurt, 60438, Germany
Abstract. The late Pliocene/early Pleistocene intensification of Northern Hemisphere Glaciation (iNHG) ~ 2.5 million years ago (Marine Isotope Stages [MIS] 100–96) stands out as the most recent major tipping point in Earth's climate history. It strongly influenced oceanographic and climatic patterns including trade-wind and upwelling strength in the Eastern Equatorial Pacific (EEP). The thermocline depth in the EEP, in turn, plays a pivotal role in the evolution of short-term climate phenomena such the El Niño-Southern Oscillation, and thus bears important consequences for the Earth's climate system. However, thermocline dynamics in the EEP during to the iNHG have yet remained unclear. While numerous studies have suggested a link between a thermocline shoaling in the EEP and Northern Hemisphere ice growth, other studies have indicated a stable thermocline depth during iNHG, thereby excluding a causal relationship between thermocline dynamics and ice-sheet growth. In light of these contradictory views, we have generated geochemical (planktic foraminiferal δ18O, δ13C and Mg/Ca), sedimentological (sand-accumulation rates) and faunal (abundance data of thermocline-dwelling foraminifera) records for Ocean Drilling Program Site 849 located in the central part of the EEP. Our records span the interval from ~ 2.75 to 2.4 Ma (MIS G7–95), which is critical for understanding thermocline dynamics during the final phase of the iNHG. They document a thermocline shoaling from ~ 2.64 to 2.55 Ma (MIS G2–101) and a relatively shallow thermocline from ~ 2.55 Ma onwards (MIS 101–95). This indicates a state change in EEP thermocline depth shortly before the final phase of iNHG. Ultimately, our data support the hypothesis that (sub-)tropical thermocline shoaling may have contributed to the development of large Northern Hemisphere ice sheets.

Citation: Jakob, K. A., Pross, J., Scholz, C., Fiebig, J., and Friedrich, O.: Thermocline state change in the Eastern Equatorial Pacific during the late Pliocene/early Pleistocene intensification of Northern Hemisphere Glaciation, Clim. Past Discuss., https://doi.org/10.5194/cp-2017-151, in review, 2017.
Kim A. Jakob et al.
Kim A. Jakob et al.
Kim A. Jakob et al.

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Short summary
Eastern Equatorial Pacific (EEP) thermocline dynamics during the intensification of Northern Hemisphere Glaciation (iNHG; ~ 2.5 Ma) have yet remained unclear. In light of this uncertainty, we have generated geochemical, faunal and sedimentological data for EEP Site 849 (~ 2.75–2.4 Ma). We record a thermocline depth state change shortly before the final phase of iNHG, which supports the hypothesis that tropical thermocline shoaling may have contributed to substantial Northern Hemisphere ice growth.
Eastern Equatorial Pacific (EEP) thermocline dynamics during the intensification of Northern...
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