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

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doi: 10.1073/pnas.0812979106
Author(s): Lazarus, David B.; Kotrc, Benjamin; Wulf, Gerwin; Schmidt, Daniela N.
Author Affiliation(s): Primary:
Museum fü4 Naturkunde, Berlin, Germany
University of Bristol, United Kingdom
Volume Title: Proceedings of the National Academy of Sciences of the United States of America
Source: Proceedings of the National Academy of Sciences of the United States of America, 106(23), p.9333-9338. Publisher: National Academy of Sciences, Washington, DC, United States. ISSN: 0027-8424 CODEN: PNASA6
Note: In English. Supplemental information/data is available in the online version of this article. 38 refs.; illus.
Summary: 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 ≈0.18 (shell volume fraction) in the basal Cenozoic to modern values of ≈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 ≈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.
Year of Publication: 2009
Research Program: DSDP Deep Sea Drilling Project
ODP Ocean Drilling Program
Key Words: 10 Paleontology, Invertebrate; 12 Stratigraphy, Historical Geology and Paleoecology; Algae; Assemblages; Atlantic Ocean; Bioavailability; Biologic evolution; Blake Nose; Blake Plateau; Cenozoic; Coevolution; Deep Sea Drilling Project; Diatoms; Eocene; Geochemical cycle; Gulf of Mexico; Holocene; Indian Ocean; Invertebrata; Latitude; Leg 10; Leg 114; Leg 115; Leg 171B; Leg 177; Marine environment; Microfossils; Miocene; Modern; Neogene; North Atlantic; Ocean Drilling Program; Oligocene; Paleo-oceanography; Paleocene; Paleogene; Paleogeography; Plankton; Planktonic taxa; Plantae; Pleistocene; Pliocene; Protista; Quaternary; Radiolaria; Shells; Silica; Silicification; Silicon; Size; Solutes; South Atlantic; Southern Ocean; Stratification; Tertiary; Upper Eocene; Upper Holocene; Upper Pleistocene
Coordinates: N200000 N260000 W0840000 W0960000
S515905 S465245 E0075341 W0330558
S131002 N050454 E0734953 E0590100
N295500 N300900 W0760600 W0763800
S540000 S405600 E0140000 E0050000
Record ID: 2011054754
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