Preprints
https://doi.org/10.5194/bg-2021-230
https://doi.org/10.5194/bg-2021-230

  18 Oct 2021

18 Oct 2021

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

Late Neogene evolution of modern deep-dwelling plankton

Flavia Boscolo-Galazzo1,a, Amy Jones2, Tom Dunkley Jones2, Katherine A. Crichton1,b, Bridget S. Wade3, and Paul N. Pearson1 Flavia Boscolo-Galazzo et al.
  • 1Cardiff University, School of Earth and Environmental Sciences, Cardiff (UK)
  • 2Birmingham University, School of Geography, Earth and Environmental Sciences, Birmingham (UK)
  • 3University College London, Department of Earth Sciences, London (UK)
  • anow at: Bergen University, Department of Earth Science and Bjerknes Center for Climate Research, Bergen (Norway)
  • bnow at: Exeter University, Department of Geography, Exeter (UK)

Abstract. The fossil record of marine microplankton provides insights into the evolutionary drivers which led to the origin of modern deep-water plankton, one of the largest component of ocean biomass. We use global abundance and biogeographic data combined with depth habitat reconstructions to determine the environmental mechanisms behind speciation in two groups of pelagic microfossils over the past 15 million years. We compare our microfossil datasets with water column profiles simulated in an Earth System model. We show that deep-living planktonic foraminiferal (zooplankton) and calcareous nannofossil (mixotroph phytoplankton) species were virtually absent globally during the peak of the middle Miocene warmth. Evolution of deep-dwelling planktonic foraminifera started from subpolar-midlatitude species during late Miocene cooling, via allopatry. Deep-dwelling species subsequently spread towards lower latitudes and further diversified via depth sympatry, establishing modern communities stratified hundreds of meters down the water column. Similarly, sub-euphotic zone specialist calcareous nannofossils become a major component of tropical and sub-tropical assemblages through the latest Miocene to early Pliocene. Our model simulations suggest that increased organic matter and oxygen availability for planktonic foraminifera, and increased nutrients and light penetration for nannoplankton, favored the evolution of new deep water niches. These conditions resulted from global cooling and the associated increase in the efficiency of the biological pump over the last 15 million years.

Flavia Boscolo-Galazzo et al.

Status: open (until 05 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-230', Anonymous Referee #1, 01 Dec 2021 reply
  • RC2: 'Comment on bg-2021-230', Anonymous Referee #2, 01 Dec 2021 reply

Flavia Boscolo-Galazzo et al.

Flavia Boscolo-Galazzo et al.

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Short summary
Deep-living organisms are a major yet poorly known component of ocean biomass. Here we reconstruct the evolution of deep-living zooplankton and phytoplankton. Deep dwelling zooplankton and phytoplankton did not occur when the ocean was several degrees warmer than today, 15 million years ago. Deep-dwelling species first evolve around 7.5 million years ago, following global climate cooling. Their evolution was driven by colder ocean temperatures allowing more food, oxygen and light at depth.
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