21 Dec 2020

21 Dec 2020

Review status: this preprint is currently under review for the journal CP.

Aptian-Albian clumped isotopes from northwest China: Cool temperatures, variable atmospheric pCO2 and regional shifts in hydrologic cycle

Dustin T. Harper1, Marina B. Suarez1,2, Jessica Uglesich2, Hailu You3,4,5, Daqing Li6, and Peter Dodson7 Dustin T. Harper et al.
  • 1Department of Geology, The University of Kansas, Lawrence, KS, U.S.A.
  • 2Department of Geological Sciences, University of Texas, San Antonio, TX, U.S.A.
  • 3Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, P.R.C.
  • 4Chinese Academy of Science Center for Excellence in Life and Paleoenvironment, Beijing, P.R.C.
  • 5College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, P.R.C.
  • 6Institute of Vertebrate Paleontology and College of Life Science and Technology, Gansu Agricultural University, Lanzhou, P.R.C.
  • 7Department of Biomedical Sciences, The University of Pennsylvania, Philadelphia, U.S.A.

Abstract. The Early Cretaceous is characterized by warm background temperatures (i.e., greenhouse climate) and carbon cycle perturbations that are often marked by Ocean Anoxic Events (OAEs) and associated shifts in the hydrologic cycle. Higher-resolution records of terrestrial and marine δ13C and δ18O (both carbonates and organics) suggest climate shifts during the Aptian-Albian, including a warm period associated with OAE 1a in the early Aptian and subsequent cold snap near the Aptian-Albian boundary prior to the Kilian and OAE 1b. Understanding the continental system is an important factor in determining the triggers and feedbacks to these events. Here, we present new paleosol carbonate stable isotopic (δ13C, δ18O and Δ47) and CALMAG weathering parameter results from the Xiagou and Zhonggou Formations (part of the Xinminpu Group in the Yujingzi Basin of NW China) spanning the Aptian-Albian. Published mean annual air temperature (MAAT) records of the Barremian-Albian from Asia are relatively cool with respect to the Early Cretaceous. However, these records are largely based on coupled δ18O measurements of dinosaur apatite phosphate (δ18Op) and carbonate (δ18Ocarb), and therefore rely on estimates of meteoric water δ18O (δ18Omw) from δ18Op. Significant shifts in the hydrologic cycle likely influenced δ18Omw in the region, complicating these MAAT estimates. Thus, temperature records independent of δ18Omw (e.g., clumped isotopes or Δ47) are desirable, and required to confirm temperatures estimated with δ18Op and δ18Oc, and to reliably determine regional shifts in δ18Omw. Primary carbonate material was identified using traditional petrography, cathodoluminescence inspection, and δ13C and δ18O subsampling. Our preliminary Δ47-based temperature reconstructions (record mean of 14.9 ºC), which we interpret as likely being representative of MAAT, match prior estimates from similar paleolatitudes of Asian MAAT (average ~15 ºC) across the Aptian-Albian. This, supported by our estimated mean atmospheric paleo-pCO2 concentration of 396 ppmv, indicates relatively cooler mid-latitude terrestrial climate. Additionally, our coupled δ18O and Δ47 records suggest shifts in the regional hydrologic cycle (i.e., ΔMAP and Δδ18Omw) that may track Aptian-Albian climate perturbations (i.e., a drying of Asian continental climate associated with the cool interval).

Dustin T. Harper et al.

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Dustin T. Harper et al.

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Aptian-Albian clumped isotopes from northwest China: Cool temperatures, variable atmospheric pCO2 and regional shifts in hydrologic cycle Harper, D. T., Suarez, M. B., Uglesich, J., You, H., Li, D., and Dodson, P.

Dustin T. Harper et al.


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Short summary
This study investigates the coupling of climate, the carbon and hydrologic cycles in Asia ~113 million years ago to provide a more complete continental perspective on a dynamic climate interval associated with global ocean anoxic events. We find relatively cool conditions, and a close coupling between the amount of CO2 in the atmosphere, air temperature and rainfall in Asia. To quantify these shifts, chemical measurements from continental soils which formed during this interval are utilized.