EGU21-13981
https://doi.org/10.5194/egusphere-egu21-13981
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Requiem for the Regolith Hypothesis: Sea-Level and Temperature Reconstructions Provide a New Template for the Middle Pleistocene Transition

Peter U. Clark, Jeremy Shakun, Yair Rosenthal, Peter Köhler, Dan Schrag, Dave Pollard, Zhengyu Liu, and Pat Bartlein
Peter U. Clark et al.
  • Oregon State University, CEOAS, Corvallis, Oregon, United States of America (clarkp@onid.orst.edu)

The Middle Pleistocene Transition (MPT) has been characterized as the transition in temperature and sea level from low-amplitude, 41-kyr variability to high-amplitude, quasi-100-kyr variability in the absence of any orbital forcing between 1.2 and 0.7 Ma. The regolith hypothesis is one of a class of hypotheses developed to explain the MPT in sea level, which has been largely inferred from d18Obenthic records. Here we use a global array of 130 sea-surface temperature (SST) records based on Mg/Ca, alkenone, and faunal proxies to reconstruct global and regional SST change over the last 4.5 Myr. Average global temperature cooled by ~6.5oC since ~3.5 Ma, with the MPT represented by a significant increase in the rate of cooling between ~1.4 and 0.8 Ma, and a change from dominant 41-kyr to dominant quasi-100-kyr frequencies at ~1.2 Ma that are well correlated with CO2 over the last 800 ka (r2=0.6). Temperature terminations after 1.2 Ma correspond to skipped obliquity beats and, for the last 800 ka, large increases in CO2. We use our global SST reconstruction to remove the temperature signal from the Ahn17 d18Obenthic stack to derive d18Oseawater. Accounting for the influence of changing temperature on the isotopic composition of ice sheets, we use the d18Oseawater record to reconstruct global sea level for the last 4.5 Myr. These results suggest sea-level minima equivalent to or lower than the LGM sea-level low stand (130 m) throughout the Pleistocene. Since inception of Northern Hemisphere glaciation ~3 Ma, sea level varied linearly with obliquity until ~1.2 Ma, when sea-level began to vary nonlinearly with obliquity, with the largest terminations occurring at the same time as temperature terminations that correspond to increasing obliquity and CO2. These results suggest that the MPT is largely a temperature phenomenon likely associated with CO2. The regolith hypothesis other hypotheses developed to explain a transition from low- to high-amplitude sea level variability during the MPT are no longer required, with the MPT change in sea-level response to obliquity likely due to modulation by CO2.

How to cite: Clark, P. U., Shakun, J., Rosenthal, Y., Köhler, P., Schrag, D., Pollard, D., Liu, Z., and Bartlein, P.: Requiem for the Regolith Hypothesis: Sea-Level and Temperature Reconstructions Provide a New Template for the Middle Pleistocene Transition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13981, https://doi.org/10.5194/egusphere-egu21-13981, 2021.

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