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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Rethinking the Global Carbon Cycle with Gas Hydrates and
Seafloor Methane Throughout Time
By
Department of Earth Sciences
and the Shell Center for
Sustainability, Rice University,
Houston, TX
Prominent negative 13C excursions characterize several past
intervals of abrupt (<100 kyr) environmental change. These
anomalies, best exemplified by the >2.5% drop across the
Paleocene/Eocene thermal maximum (PETM) ca. 55.5 Ma, command
our attention because they lack explanation with conventional
models for global carbon cycling. Increasingly, Earth
scientists have argued that they signify massive
release of CH4 from marine gas
hydrates, although typically without considering
the underlying process or the ensuing
ramifications of such an interpretation. At
the most basic level, a large, dynamic “gas
hydrate capacitor” stores and releases 13C-depleted
carbon at rates linked to external
conditions such as deep ocean temperature.
The capacitor contains three internal
reservoirs: dissolved gas, gas hydrate, and
free gas. Carbon enters and leaves these
reservoirs through microbial decomposition
of organic matter, anaerobic oxidation of
CH4 in shallow sediment, and seafloor gas venting; carbon cycles
between these reservoirs through several processes, including
fluid flow, precipitation and dissolution of gas hydrate, and
burial. Numerical simulations show that simple gas hydrate
capacitors driven by inferred changes in bottom
water warming
during the PETM can generate a global 13C excursion that
mimics observations. The same modeling extended over longer
time demonstrates that variable CH4 fluxes to and from gas
hydrates can partly explain other 13C excursions, rapid and
slow, large and small, negative and positive. Although such
modeling is rudimentary (because processes and variables in
modern and ancient gas hydrate systems remain poorly
constrained), acceptance of a vast, externally regulated gas
hydrate capacitor forces us to rethink 13C records and the
operation of the global carbon cycle throughout time.
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