Radiolarians decreased silicification as an evolutionary response to reduced Cenozoic ocean silica availability

David B Lazarus, Benjamin Kotrc, Gerwin Wulf, Daniela N Schmidt

Research output: Contribution to journalArticle (Academic Journal)peer-review

51 Citations (Scopus)

Abstract

It has been hypothesized that increased water column stratification has been an abiotic "universal driver" affecting average cell size in Cenozoic marine plankton. Gradually decreasing Cenozoic radiolarian shell weight, by contrast, suggests that competition for dissolved silica, a shared nutrient, resulted in biologic coevolution between radiolaria and marine diatoms, which expanded dramatically in the Cenozoic. We present data on the 2 components of shell weight change--size and silicification--of Cenozoic radiolarians. In low latitudes, increasing Cenozoic export of silica to deep waters by diatoms and decreasing nutrient upwelling from increased water column stratification have created modern silica-poor surface waters. Here, radiolarian silicification decreases significantly (r = 0.91, P <0.001), from approximately 0.18 (shell volume fraction) in the basal Cenozoic to modern values of approximately 0.06. A third of the total change occurred rapidly at 35 Ma, in correlation to major increases in water column stratification and abundance of diatoms. In high southern latitudes, Southern Ocean circulation, present since the late Eocene, maintains significant surface water silica availability. Here, radiolarian silicification decreased insignificantly (r = 0.58, P = 0.1), from approximately 0.13 at 35 Ma to 0.11 today. Trends in shell size in both time series are statistically insignificant and are not correlated with each other. We conclude that there is no universal driver changing cell size in Cenozoic marine plankton. Furthermore, biologic and physical factors have, in concert, by reducing silica availability in surface waters, forced macroevolutionary changes in Cenozoic low-latitude radiolarians.
Translated title of the contributionRadiolarians decreased silicification as an evolutionary response to reduced Cenozoic ocean silica availability
Original languageEnglish
Pages (from-to)9333 - 9328
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume106
Issue number23
DOIs
Publication statusPublished - 9 Jun 2009

Bibliographical note

Author of Publication Reviewed: Lazarus, D., Kotrc, B., Wulf, G. and Schmidt, D.N

Keywords

  • Ecosystem
  • Animals
  • Biological Evolution
  • Diatoms
  • Silicon Dioxide
  • Plankton

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