30
H. Khozyem
PETM is marked by increased detrital input and kaolinite contents due to intense
on-land weathering during the hot humid climate [106, 107]. In the terrestrial realm,
it led to the diversification of modern mammal species and their migration across
the northern continents [108–110] many of which immigrated to the North American continent during the greenhouse warming [110]. Moreover, [111] hypothesized
that the temperature and precipitation changes associated with the PETM stimulated
rapid shifts in plant community composition.
The PETM is marked by a large negative carbon isotope excursion (CIE) in
terrestrial and marine carbonates and organic matter [99, 112, 113, 110], reflecting
a rapid release of
13 C-depleted carbon into the ocean-atmosphere system due to
injection of huge amount of CO 2 into the atmosphere estimated to reach about 2000–
2600 Gt over 10 ka [96]. There are many potential sources of CO 2 during the PETM
and many scenarios have been proposed to explain the injection of high amounts of
CO 2 [96] in both marine and atmospheric ecosystems leading subsequently to the
perturbation of the carbon cycle from the latest of Paleocene into the earliest Eocene.
More than twenty-five years and hundreds of studies of both surface and subsurface
sections covering the PETM interval yielded five main hypotheses were summarized
[114].
Wildfires: Burning of the extensive peat and coal deposited during the Paleocene
(δ
13 C of ~−22‰) could have resulted from increasing atmospheric O 2 , dryer climate,
and/or uplift of coal basins [42]. However, no increase in combustion byproducts was
observed in cores from neither the Atlantic nor Pacific [115].
Thermogenic methane: Injection of magma into organic-rich sediments could
have caused the explosive release of thermogenic methane (δ
13 C of ∼−30‰) from
Cretaceous-Paleocene mudstones in the North Atlantic [43, 44, 116, 45].
Drying epicontinental seas: Tectonically driven isolation of an epicontinental seaway could have led to rapid (<20 ka) desiccation and oxidation of organic matter
(δ
13 C of ∼−22‰) [46]. However, shallow seaways of the Paleocene-Eocene covered
vast areas of central Asia, and none are known to have dried up coincident with the
PETM [117]
Permafrost: During the Paleogene, Antarctica did not support a large ice cap and
may have stored huge quantities of carbon as permafrost and peat that could have
been rapidly defrosted and oxidized, releasing carbon (δ
13 C of ∼−30‰) [47].
Catastrophic methane release: the most recognized scenario explaining the PETM
event is the catastrophic methane release from hydrates (clathrates) [48, 49].
This scenario invokes methane released from the continental margin that could
have led to carbon dioxide input estimated at 2000 × 10
9 metric tons over
10,000 years [118], which was suggested as potentially the main cause for the PETM
[119, 120]. Clathrates are stable in deep-sea sediments but can be destabilized by
increasing temperature caused by changes in ocean circulation [48, 121] by decreasing pressure resulting from slope failure [97] or sea level changes. The clathrate
release could also result from late Paleocene volcanic activities linked to the opening
of the North Atlantic Ocean [122, 9]. Whatever the source of CO 2 released during the
H. Khozyem
PETM is marked by increased detrital input and kaolinite contents due to intense
on-land weathering during the hot humid climate [106, 107]. In the terrestrial realm,
it led to the diversification of modern mammal species and their migration across
the northern continents [108–110] many of which immigrated to the North American continent during the greenhouse warming [110]. Moreover, [111] hypothesized
that the temperature and precipitation changes associated with the PETM stimulated
rapid shifts in plant community composition.
The PETM is marked by a large negative carbon isotope excursion (CIE) in
terrestrial and marine carbonates and organic matter [99, 112, 113, 110], reflecting
a rapid release of
13 C-depleted carbon into the ocean-atmosphere system due to
injection of huge amount of CO 2 into the atmosphere estimated to reach about 2000–
2600 Gt over 10 ka [96]. There are many potential sources of CO 2 during the PETM
and many scenarios have been proposed to explain the injection of high amounts of
CO 2 [96] in both marine and atmospheric ecosystems leading subsequently to the
perturbation of the carbon cycle from the latest of Paleocene into the earliest Eocene.
More than twenty-five years and hundreds of studies of both surface and subsurface
sections covering the PETM interval yielded five main hypotheses were summarized
[114].
Wildfires: Burning of the extensive peat and coal deposited during the Paleocene
(δ
13 C of ~−22‰) could have resulted from increasing atmospheric O 2 , dryer climate,
and/or uplift of coal basins [42]. However, no increase in combustion byproducts was
observed in cores from neither the Atlantic nor Pacific [115].
Thermogenic methane: Injection of magma into organic-rich sediments could
have caused the explosive release of thermogenic methane (δ
13 C of ∼−30‰) from
Cretaceous-Paleocene mudstones in the North Atlantic [43, 44, 116, 45].
Drying epicontinental seas: Tectonically driven isolation of an epicontinental seaway could have led to rapid (<20 ka) desiccation and oxidation of organic matter
(δ
13 C of ∼−22‰) [46]. However, shallow seaways of the Paleocene-Eocene covered
vast areas of central Asia, and none are known to have dried up coincident with the
PETM [117]
Permafrost: During the Paleogene, Antarctica did not support a large ice cap and
may have stored huge quantities of carbon as permafrost and peat that could have
been rapidly defrosted and oxidized, releasing carbon (δ
13 C of ∼−30‰) [47].
Catastrophic methane release: the most recognized scenario explaining the PETM
event is the catastrophic methane release from hydrates (clathrates) [48, 49].
This scenario invokes methane released from the continental margin that could
have led to carbon dioxide input estimated at 2000 × 10
9 metric tons over
10,000 years [118], which was suggested as potentially the main cause for the PETM
[119, 120]. Clathrates are stable in deep-sea sediments but can be destabilized by
increasing temperature caused by changes in ocean circulation [48, 121] by decreasing pressure resulting from slope failure [97] or sea level changes. The clathrate
release could also result from late Paleocene volcanic activities linked to the opening
of the North Atlantic Ocean [122, 9]. Whatever the source of CO 2 released during the