Sylvain Richoz
Senior lecturer
Global perturbation of the marine calcium cycle during the Permian-Triassic transition
Author
Summary, in English
A negative shift in the calcium isotopic
composition of marine carbonate rocks
spanning the end-Permian extinction horizon
in South China has been used to argue
for an ocean acidification event coincident
with mass extinction. This interpretation
has proven controversial, both because the
excursion has not been demonstrated across
multiple, widely separated localities, and because
modeling results of coupled carbon and
calcium isotope records illustrate that calcium
cycle imbalances alone cannot account
for the full magnitude of the isotope excursion.
Here, we further test potential controls
on the Permian-Triassic calcium isotope
record by measuring calcium isotope ratios
from shallow-marine carbonate successions
spanning the Permian-Triassic boundary in
Turkey, Italy, and Oman. All measured sections
display negative shifts in δ44/40Ca of up
to 0.6‰. Consistency in the direction, magnitude,
and timing of the calcium isotope excursion
across these widely separated localities
implies a primary and global δ44/40Ca signature.
Based on the results of a coupled box
model of the geological carbon and calcium
cycles, we interpret the excursion to reflect a
series of consequences arising from volcanic
CO2 release, including a temporary decrease
in seawater δ44/40Ca due to short-lived ocean
acidification and a more protracted increase
in calcium isotope fractionation associated
with a shift toward more primary aragonite
in the sediment and, potentially, subsequently
elevated carbonate saturation states
caused by the persistence of elevated CO2
delivery from volcanism. Locally, changing
balances between aragonite and calcite production
are sufficient to account for the calcium
isotope excursions, but this effect alone
does not explain the globally observed negative
excursion in the δ13C values of carbonate
sediments and organic matter as well. Only
a carbon release event and related geochemical
consequences are consistent both with
calcium and carbon isotope data. The carbon
release scenario can also account for oxygen
isotope evidence for dramatic and protracted
global warming as well as paleontological
evidence
for the preferential extinction of
marine animals most susceptible to acidification,
warming, and anoxia.
composition of marine carbonate rocks
spanning the end-Permian extinction horizon
in South China has been used to argue
for an ocean acidification event coincident
with mass extinction. This interpretation
has proven controversial, both because the
excursion has not been demonstrated across
multiple, widely separated localities, and because
modeling results of coupled carbon and
calcium isotope records illustrate that calcium
cycle imbalances alone cannot account
for the full magnitude of the isotope excursion.
Here, we further test potential controls
on the Permian-Triassic calcium isotope
record by measuring calcium isotope ratios
from shallow-marine carbonate successions
spanning the Permian-Triassic boundary in
Turkey, Italy, and Oman. All measured sections
display negative shifts in δ44/40Ca of up
to 0.6‰. Consistency in the direction, magnitude,
and timing of the calcium isotope excursion
across these widely separated localities
implies a primary and global δ44/40Ca signature.
Based on the results of a coupled box
model of the geological carbon and calcium
cycles, we interpret the excursion to reflect a
series of consequences arising from volcanic
CO2 release, including a temporary decrease
in seawater δ44/40Ca due to short-lived ocean
acidification and a more protracted increase
in calcium isotope fractionation associated
with a shift toward more primary aragonite
in the sediment and, potentially, subsequently
elevated carbonate saturation states
caused by the persistence of elevated CO2
delivery from volcanism. Locally, changing
balances between aragonite and calcite production
are sufficient to account for the calcium
isotope excursions, but this effect alone
does not explain the globally observed negative
excursion in the δ13C values of carbonate
sediments and organic matter as well. Only
a carbon release event and related geochemical
consequences are consistent both with
calcium and carbon isotope data. The carbon
release scenario can also account for oxygen
isotope evidence for dramatic and protracted
global warming as well as paleontological
evidence
for the preferential extinction of
marine animals most susceptible to acidification,
warming, and anoxia.
Department/s
- Lithosphere and Biosphere Science
Publishing year
2018-01-08
Language
English
Pages
1323-1338
Publication/Series
Geological Society of America Bulletin
Volume
130
Issue
7-8
Links
Document type
Journal article
Publisher
Geological Society of America
Topic
- Geology
Status
Published
ISBN/ISSN/Other
- ISSN: 0016-7606