Preprints
https://doi.org/10.5194/cp-2021-122
https://doi.org/10.5194/cp-2021-122

  17 Sep 2021

17 Sep 2021

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

Late Paleocene CO2 drawdown, climatic cooling, and terrestrial denudation in the southwest Pacific

Christopher J. Hollis1,2, Sebastian Naeher1, Christopher D. Clowes1, Jenny Dahl1, Xun Li1, B. David A. Naafs3, Richard D. Pancost3, Kyle W. R. Taylor3, G. Todd Ventura1,4, and Richard Sykes1 Christopher J. Hollis et al.
  • 1GNS Science, Lower Hutt, 5040, New Zealand
  • 2Victoria University of Wellington, Wellington, New Zealand
  • 3Organic Geochemistry Unit, School of Chemistry, School of Earth Sciences, and Cabot Institute for the Environment, University of Bristol, Bristol, UK
  • 4Department of Geology, Saint Mary's University, Halifax, Nova Scotia, Canada

Abstract. Late Paleocene deposition of an organic-rich sedimentary facies on the continental shelf and slope of New Zealand and eastern Australia has been linked to short-lived climatic cooling and terrestrial denudation following sea-level fall. Recent studies have confirmed that the organic matter in this facies, termed Waipawa organofacies, is primarily of terrestrial origin, with a minor marine component. It is also unusually enriched in δ13C. In this study we aim to determine the cause or causes of this enrichment. For Waipawa organofacies and its bounding facies in the Taylor White section, Hawkes Bay, paired palynofacies and δ13C analysis of density fractions indicate that the heaviest δ13C values are associated with degraded phytoclasts (woody plant matter) and that the 13C enrichment is partly due to lignin degradation. Compound specific δ13C analyses of samples from the Taylor White and mid-Waipara (Canterbury) sections confirms this relationship but also reveal a residual 13C enrichment of ~ 2.5 ‰ in higher plant biomarkers (n-alkanes and n-alkanoic acids) and 3–4 ‰ in the subordinate marine component, which we interpret as indicating a significant drawdown of atmospheric CO2.

Refined age control for Waipawa organofacies indicates that deposition occurred between 59.2 and 58.4 Ma, which coincides with a Paleocene oxygen isotope maximum (POIM) and the onset of the Paleocene carbon isotope maximum (PCIM). This timing suggests that this depositional event was related to global cooling and carbon burial. This relationship is further supported by published TEX86-based sea surface temperatures that indicate a pronounced regional cooling during deposition. We suggest that reduced greenhouse gas emissions from volcanism and accelerated carbon burial related to several tectonic factors and positive feedbacks resulted in short-lived global cooling, growth of ephemeral ice sheets, and a global fall in sea level. Accompanying erosion and carbonate dissolution in deep sea sediment archives may have hidden the evidence of this "hypothermal" event until now.

Christopher J. Hollis et al.

Status: open (until 12 Nov 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on cp-2021-122', Steve Killops, 30 Sep 2021 reply
  • RC1: 'Comment on cp-2021-122', Peter Bijl, 14 Oct 2021 reply
  • RC2: 'Comment on cp-2021-122', Anonymous Referee #2, 21 Oct 2021 reply

Christopher J. Hollis et al.

Christopher J. Hollis et al.

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Short summary
Previous studies of Paleogene greenhouse climates identified short-lived global warming events, termed hyperthermals, that provide insights into global warming scenarios. Within the same time period, we have identified a short-lived cooling event in the late Paleocene, which we term a hypothermal, that has potential to provide novel insights into the feedback mechanisms at work in a greenhouse climate.