Preprints
https://doi.org/10.5194/cp-2023-29
https://doi.org/10.5194/cp-2023-29
23 May 2023
 | 23 May 2023
Status: a revised version of this preprint was accepted for the journal CP and is expected to appear here in due course.

Nonlinear increase in seawater 87Sr/86Sr in the Oligocene to early Miocene and implications for climate-sensitive weathering

Heather M. Stoll, Leopoldo D. Pena, Ivan Hernandez-Almeida, José Guitián, Thomas Tanner, and Heiko Paelike

Abstract. The 87Sr/86Sr of marine carbonates provides a key constraint on the balance of continental weathering and hydrothermal Sr fluxes to the ocean, and mid-Oligocene to mid-Miocene features the most rapid rates of increase in the 87Sr/86Sr of the Cenozoic. Because previous records of the 87Sr/86Sr increase with time were based on biostratigraphically defined age models in diverse locations, it was difficult to unambigiously distinguish m.y. scale variations in the rate of 87Sr/86Sr change from variations in sedimentation rate. In this study, we produce the first 87Sr/86Sr results from an Oligocene to early Miocene site with a precise age model derived orbital tuning of high resolution benthic δ18O, at the Equatorial Pacific Ocean Drilling Program (ODP) Site 1218. Our new dataset resolves transient decreases in 87Sr/86Sr, as well as periods of relative stasis. These changes can be directly compared with the high resolution benthic δ18O in the same site. We find slowing of the rate of 87Sr/86Sr increase coincides with the onset of Antarctic ice expansion at the beginning of the Mid-Oligocene Glacial Interval, and a rapid steeping in the 87Sr/86Sr increase coincides with the benthic δ18O evidence for rapid ice retreat. This pattern may reflect either northward shifts in the Intertropical Convergence Zone precipitation to areas of nonradiogenic bedrock, and/or lowered weathering fluxes from highly radiogenic glacial flours on Antarctic. We additionally generate the first 87Sr/86Sr data from ODP Site 1168 and International Ocean Discovery Program (IODP) Site 1406 during the Oligocene to early Miocene to improve the precision of age correlation of these Northern Hemisphere and Southern Hemisphere mid-latitude sites, and to better estimate the duration of early Miocene hiatus and condensed sedimentation.

Heather M. Stoll et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2023-29', Anonymous Referee #1, 20 Jun 2023
    • AC2: 'Reply on RC1', Heather Stoll, 25 Aug 2023
  • RC2: 'Comment on cp-2023-29', Anonymous Referee #1, 20 Jun 2023
    • AC1: 'Reply on RC2', Heather Stoll, 25 Aug 2023
  • CC1: 'Comment on cp-2023-29', Derry, 21 Jun 2023
    • AC3: 'Reply on CC1', Heather Stoll, 25 Aug 2023

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2023-29', Anonymous Referee #1, 20 Jun 2023
    • AC2: 'Reply on RC1', Heather Stoll, 25 Aug 2023
  • RC2: 'Comment on cp-2023-29', Anonymous Referee #1, 20 Jun 2023
    • AC1: 'Reply on RC2', Heather Stoll, 25 Aug 2023
  • CC1: 'Comment on cp-2023-29', Derry, 21 Jun 2023
    • AC3: 'Reply on CC1', Heather Stoll, 25 Aug 2023

Heather M. Stoll et al.

Heather M. Stoll et al.

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Short summary
The Oligocene and Early Miocene periods featured dynamic glacial cycles on Antarctica. In this paper, we use Sr isotopes in marine carbonate sediments to document a change in the location and intensity of continental weathering during short periods of very intense Antartic glaciation. Potentially, the weathering intensity of old continental rocks on Antarctica was reduced during glaciation. We also show improved age models for correlation of Southern ocean and North Atlantic sediments.