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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 7 | Copyright
Clim. Past, 14, 1079-1095, 2018
https://doi.org/10.5194/cp-14-1079-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Jul 2018

Research article | 25 Jul 2018

Thermocline state change in the eastern equatorial Pacific during the late Pliocene/early Pleistocene intensification of Northern Hemisphere glaciation

Kim Alix Jakob1, Jörg Pross1, Christian Scholz1, Jens Fiebig2, and Oliver Friedrich1 Kim Alix Jakob et al.
  • 1Institute of Earth Sciences, Heidelberg University, 69120 Heidelberg, Germany
  • 2Institute of Geosciences, Goethe University Frankfurt, 60438 Frankfurt, 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 an important tipping point in Earth's climate history, which 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 Earth's climate system: small changes in its depth associated with short-term climate phenomena such as the El Niño–Southern Oscillation can affect surface-water properties and the ocean–atmosphere exchange. However, thermocline dynamics in the EEP during the iNHG still remain 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 the iNHG; consequently, a causal relationship between thermocline dynamics and ice-sheet growth has been excluded. In light of these contradictory views, we have generated geochemical (planktic foraminiferal δ18O, δ13C and MgCa), sedimentological (sand accumulation rates) and faunal (abundance data of thermocline-dwelling foraminifera) records for Ocean Drilling Program Site 849 located in the central region of the EEP. Our records span the interval from  ∼ 2.75 to 2.4Ma (MIS G7–95), which is critical for understanding thermocline dynamics during the final phase of the iNHG. Our new records document a thermocline shoaling from  ∼ 2.64 to 2.55Ma (MIS G2–101) and a relatively shallow thermocline from  ∼ 2.55Ma onwards (MIS 101–95). This indicates a state change in thermocline depth at Site 849 shortly before the final phase of the iNHG. Ultimately, our data support the hypothesis that (sub-)tropical thermocline shoaling may have contributed to the development of large Northern Hemisphere ice sheets.

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Eastern equatorial Pacific (EEP) thermocline dynamics during the intensification of Northern Hemisphere glaciation (iNHG; ~ 2.5 Ma) currently remain unclear. In light of this uncertainty, we generated geochemical, faunal and sedimentological data for EEP Site 849 (~ 2.75–2.4 Ma). We recorded a thermocline depth change shortly before the final phase of the 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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