02 May 2022
02 May 2022
Status: this preprint is currently under review for the journal BG.

Nature and origin of variations in pelagic carbonate production in the tropical ocean since the Mid Miocene (ODP Site 927)

Pauline Cornuault1, Thomas Westerhold1, Heiko Pälike1, Torsten Bickert1, Karl-Heinz Baumann2, and Michal Kucera1 Pauline Cornuault et al.
  • 1University of Bremen, MARUM - Centre for Marine Environmental Sciences, Leobener Straße 8, D-28359 Bremen, Germany
  • 2University of Bremen, Geoscience Department, Klagenfurter Straße, PO Box 330440, 28359 Bremen, Germany

Abstract. Marine plankton is an important component of the global carbon cycle. Whereas the production and seafloor export of organic carbon produced by the plankton, the biological pump, has received much attention, the long-term variability in plankton calcification, controlling the carbonate counter pump, remains less well understood. Yet, it has been shown that on geological time scales, changes in pelagic calcification (biological compensation) could affect the ocean's buffering capacity and thus regulate global carbon budget. Here we use Neogene pelagic sediments deposited on the Ceara Rise in the tropical Atlantic to characterise the variability in pelagic carbonate production with focus on warm climates. A re-evaluation of published records of carbonate accumulation at Ceara Rise reveals a systematic increase in sedimentation rates since the late Miocene, but the carbonate accumulation rate does not show a clear trend. Instead, we observe substantial orbital time-scale variability in carbonate accumulation and an effect of carbonate preservation, especially at sites located below 4 km. To evaluate long-term changes against possible orbital-scale variability, we generated new high-resolution records of carbonate accumulation rate at ODP Site 927 across two Quaternary interglacials (MIS 5 and MIS 9), the Pliocene warm period (MIS KM5) and the Miocene climate optimum (MCO). We observe that the highest carbonate accumulation rates occurred during the Pliocene but that each interval was characterised by large orbital-scale variability. Prominent variations in carbonate accumulation prior to the Quaternary preservation cycles appear to follow obliquity and eccentricity. These results imply that pelagic carbonate production in the tropical ocean, buffered from large temperature changes, varied on orbital time scales similarly or even more than on longer time scales. Since preservation can be excluded as a driver of these changes prior to the Quaternary, the observed variations must reflect changes in the export flux of pelagic biogenic carbonate. We conclude that the overall carbonate production by pelagic calcifiers responded to local changes in light, temperature and nutrients delivered by upwelling, which followed long orbital cycles, as well as to long-term shifts in climate and/or ocean chemistry. The inferred changes on both time scales were sufficiently large such that when extrapolated on a global scale, they could have played a role in the regulation of the carbon cycle and global climate evolution during the transition from the Miocene warm climates into the Quaternary icehouse.

Pauline Cornuault et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-81', Anonymous Referee #1, 27 Jun 2022
    • AC1: 'Reply on RC1', Pauline Cornuault, 12 Sep 2022
  • RC2: 'Comment on bg-2022-81', Anonymous Referee #2, 25 Jul 2022
    • AC2: 'Reply on RC2', Pauline Cornuault, 12 Sep 2022

Pauline Cornuault et al.

Pauline Cornuault et al.


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Short summary
We generated high-resolution records of carbonate accumulation rate from Miocene to Quaternary in the tropical Atlantic Ocean to characterise the variability in pelagic carbonate production during warm climate. It follows orbital cycles, responding to local changes in tropical conditions as well as to long-term shifts in climate and ocean chemistry. These changes were sufficiently large to play a role in the carbon cycle and global climate evolution.