Bioturbation and directionality in Earth's carbon isotope record across the Neoproterozoic–Cambrian transition

R. A. Boyle*, T. W. Dahl, C. J. Bjerrum, D. E. Canfield

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

57 Downloads (Pure)

Abstract

Mixing of sediments by moving animals becomes apparent in the trace fossil record from about 550 million years ago (Ma), loosely overlapping with the tail end of the extreme carbonate carbon isotope δ13Ccarbonate fluctuations that qualitatively distinguish the Proterozoic geochemical record from that of the Phanerozoic. These Precambrian-scale fluctuations in δ13Ccarbonate (PSF-δ13Ccarbonate) remain enigmatic, due to their high amplitude and inclusion of global-scale negative δ13Ccarbonate values, below anything attributable to mantle input. Here, we note that different biogeochemical-model scenarios plausibly explaining globally synchronous PSF-δ13Ccarbonate converge: via mechanistic requirements for extensive anoxia in marine sediments to support sedimentary build-up of 13C-depleted carbon. We hypothesize that bioturbation qualitatively reduced marine sediment anoxia by exposing sediments to oxygenated overlying waters, which ultimately contributed to decreasing the carbon cycle's subsequent susceptibility to PSF- δ13Ccarbonate. Bioturbation may also have reduced the quantity of (isotopically light) organic-derived carbon available to contribute to PSF- δ13Ccarbonate via ocean crust carbonatization at depth. We conduct a comparative modelling exercise in which we introduce bioturbation to existing model scenarios for PSF- δ13Ccarbonate: expressing both the anoxic proportion of marine sediments, and the global organic carbon burial efficiency, as a decreasing function of bioturbation. We find that bioturbation's oxygenating impact on sediments has the capacity to prevent PSF- δ13Ccarbonate caused by authigenic carbonate precipitation or methanogenesis. Bioturbation's impact on the f-ratio via remineralization is partially offset by liberation of organic phosphate, some of which feeds back into new production. We emphasize that this study is semiquantitative, exploratory and intended merely to provide a qualitative theoretical framework within which bioturbation's impact on long-term, first-order δ13Ccarbonate can be assessed (and it is hoped quantified in more detail by future work). With this proviso, we conclude that it is entirely plausible that bioturbation made a decisive contribution to the enigmatic directionality in the δ13Ccarbonate record, from the Neoproterozoic–Cambrian boundary onwards.

Original languageEnglish
JournalGeobiology
Volume16
Issue number3
Pages (from-to)252-278
ISSN1472-4677
DOIs
Publication statusPublished - May 2018

Fingerprint

bioturbation
carbon isotope
isotopes
carbon
marine sediments
marine sediment
anoxia
sediments
carbonates
hypoxia
Precambrian
phosphate (organic)
sediment
carbonate
remineralization
trace fossil
methanogenesis
methane production
Phanerozoic
fossil record

Keywords

  • biogeochemistry
  • bioturbation
  • cambrian substrate revolution
  • carbon isotope record
  • evolution
  • Neoproterozoic
  • Anaerobiosis
  • Metabolism
  • Fossils
  • Carbon Cycle
  • Computer Simulation
  • Geologic Sediments/chemistry
  • Carbon Isotopes/analysis

Cite this

@article{5240970340d649419866ba667016bc6f,
title = "Bioturbation and directionality in Earth's carbon isotope record across the Neoproterozoic–Cambrian transition",
abstract = "Mixing of sediments by moving animals becomes apparent in the trace fossil record from about 550 million years ago (Ma), loosely overlapping with the tail end of the extreme carbonate carbon isotope δ13Ccarbonate fluctuations that qualitatively distinguish the Proterozoic geochemical record from that of the Phanerozoic. These Precambrian-scale fluctuations in δ13Ccarbonate (PSF-δ13Ccarbonate) remain enigmatic, due to their high amplitude and inclusion of global-scale negative δ13Ccarbonate values, below anything attributable to mantle input. Here, we note that different biogeochemical-model scenarios plausibly explaining globally synchronous PSF-δ13Ccarbonate converge: via mechanistic requirements for extensive anoxia in marine sediments to support sedimentary build-up of 13C-depleted carbon. We hypothesize that bioturbation qualitatively reduced marine sediment anoxia by exposing sediments to oxygenated overlying waters, which ultimately contributed to decreasing the carbon cycle's subsequent susceptibility to PSF- δ13Ccarbonate. Bioturbation may also have reduced the quantity of (isotopically light) organic-derived carbon available to contribute to PSF- δ13Ccarbonate via ocean crust carbonatization at depth. We conduct a comparative modelling exercise in which we introduce bioturbation to existing model scenarios for PSF- δ13Ccarbonate: expressing both the anoxic proportion of marine sediments, and the global organic carbon burial efficiency, as a decreasing function of bioturbation. We find that bioturbation's oxygenating impact on sediments has the capacity to prevent PSF- δ13Ccarbonate caused by authigenic carbonate precipitation or methanogenesis. Bioturbation's impact on the f-ratio via remineralization is partially offset by liberation of organic phosphate, some of which feeds back into new production. We emphasize that this study is semiquantitative, exploratory and intended merely to provide a qualitative theoretical framework within which bioturbation's impact on long-term, first-order δ13Ccarbonate can be assessed (and it is hoped quantified in more detail by future work). With this proviso, we conclude that it is entirely plausible that bioturbation made a decisive contribution to the enigmatic directionality in the δ13Ccarbonate record, from the Neoproterozoic–Cambrian boundary onwards.",
keywords = "biogeochemistry, bioturbation, cambrian substrate revolution, carbon isotope record, evolution, Neoproterozoic, Anaerobiosis, Metabolism, Fossils, Carbon Cycle, Computer Simulation, Geologic Sediments/chemistry, Carbon Isotopes/analysis",
author = "Boyle, {R. A.} and Dahl, {T. W.} and Bjerrum, {C. J.} and Canfield, {D. E.}",
year = "2018",
month = "5",
doi = "10.1111/gbi.12277",
language = "English",
volume = "16",
pages = "252--278",
journal = "Geobiology",
issn = "1472-4677",
publisher = "Wiley-Blackwell",
number = "3",

}

Bioturbation and directionality in Earth's carbon isotope record across the Neoproterozoic–Cambrian transition. / Boyle, R. A.; Dahl, T. W.; Bjerrum, C. J.; Canfield, D. E.

In: Geobiology, Vol. 16, No. 3, 05.2018, p. 252-278.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Bioturbation and directionality in Earth's carbon isotope record across the Neoproterozoic–Cambrian transition

AU - Boyle, R. A.

AU - Dahl, T. W.

AU - Bjerrum, C. J.

AU - Canfield, D. E.

PY - 2018/5

Y1 - 2018/5

N2 - Mixing of sediments by moving animals becomes apparent in the trace fossil record from about 550 million years ago (Ma), loosely overlapping with the tail end of the extreme carbonate carbon isotope δ13Ccarbonate fluctuations that qualitatively distinguish the Proterozoic geochemical record from that of the Phanerozoic. These Precambrian-scale fluctuations in δ13Ccarbonate (PSF-δ13Ccarbonate) remain enigmatic, due to their high amplitude and inclusion of global-scale negative δ13Ccarbonate values, below anything attributable to mantle input. Here, we note that different biogeochemical-model scenarios plausibly explaining globally synchronous PSF-δ13Ccarbonate converge: via mechanistic requirements for extensive anoxia in marine sediments to support sedimentary build-up of 13C-depleted carbon. We hypothesize that bioturbation qualitatively reduced marine sediment anoxia by exposing sediments to oxygenated overlying waters, which ultimately contributed to decreasing the carbon cycle's subsequent susceptibility to PSF- δ13Ccarbonate. Bioturbation may also have reduced the quantity of (isotopically light) organic-derived carbon available to contribute to PSF- δ13Ccarbonate via ocean crust carbonatization at depth. We conduct a comparative modelling exercise in which we introduce bioturbation to existing model scenarios for PSF- δ13Ccarbonate: expressing both the anoxic proportion of marine sediments, and the global organic carbon burial efficiency, as a decreasing function of bioturbation. We find that bioturbation's oxygenating impact on sediments has the capacity to prevent PSF- δ13Ccarbonate caused by authigenic carbonate precipitation or methanogenesis. Bioturbation's impact on the f-ratio via remineralization is partially offset by liberation of organic phosphate, some of which feeds back into new production. We emphasize that this study is semiquantitative, exploratory and intended merely to provide a qualitative theoretical framework within which bioturbation's impact on long-term, first-order δ13Ccarbonate can be assessed (and it is hoped quantified in more detail by future work). With this proviso, we conclude that it is entirely plausible that bioturbation made a decisive contribution to the enigmatic directionality in the δ13Ccarbonate record, from the Neoproterozoic–Cambrian boundary onwards.

AB - Mixing of sediments by moving animals becomes apparent in the trace fossil record from about 550 million years ago (Ma), loosely overlapping with the tail end of the extreme carbonate carbon isotope δ13Ccarbonate fluctuations that qualitatively distinguish the Proterozoic geochemical record from that of the Phanerozoic. These Precambrian-scale fluctuations in δ13Ccarbonate (PSF-δ13Ccarbonate) remain enigmatic, due to their high amplitude and inclusion of global-scale negative δ13Ccarbonate values, below anything attributable to mantle input. Here, we note that different biogeochemical-model scenarios plausibly explaining globally synchronous PSF-δ13Ccarbonate converge: via mechanistic requirements for extensive anoxia in marine sediments to support sedimentary build-up of 13C-depleted carbon. We hypothesize that bioturbation qualitatively reduced marine sediment anoxia by exposing sediments to oxygenated overlying waters, which ultimately contributed to decreasing the carbon cycle's subsequent susceptibility to PSF- δ13Ccarbonate. Bioturbation may also have reduced the quantity of (isotopically light) organic-derived carbon available to contribute to PSF- δ13Ccarbonate via ocean crust carbonatization at depth. We conduct a comparative modelling exercise in which we introduce bioturbation to existing model scenarios for PSF- δ13Ccarbonate: expressing both the anoxic proportion of marine sediments, and the global organic carbon burial efficiency, as a decreasing function of bioturbation. We find that bioturbation's oxygenating impact on sediments has the capacity to prevent PSF- δ13Ccarbonate caused by authigenic carbonate precipitation or methanogenesis. Bioturbation's impact on the f-ratio via remineralization is partially offset by liberation of organic phosphate, some of which feeds back into new production. We emphasize that this study is semiquantitative, exploratory and intended merely to provide a qualitative theoretical framework within which bioturbation's impact on long-term, first-order δ13Ccarbonate can be assessed (and it is hoped quantified in more detail by future work). With this proviso, we conclude that it is entirely plausible that bioturbation made a decisive contribution to the enigmatic directionality in the δ13Ccarbonate record, from the Neoproterozoic–Cambrian boundary onwards.

KW - biogeochemistry

KW - bioturbation

KW - cambrian substrate revolution

KW - carbon isotope record

KW - evolution

KW - Neoproterozoic

KW - Anaerobiosis

KW - Metabolism

KW - Fossils

KW - Carbon Cycle

KW - Computer Simulation

KW - Geologic Sediments/chemistry

KW - Carbon Isotopes/analysis

U2 - 10.1111/gbi.12277

DO - 10.1111/gbi.12277

M3 - Journal article

VL - 16

SP - 252

EP - 278

JO - Geobiology

JF - Geobiology

SN - 1472-4677

IS - 3

ER -