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| Titel |
Greenhouse atmospheric hydrology and polar warmth during the mid-Cretaceous and PETM |
| VerfasserIn |
T. White, D. Pollard |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250031160
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| Zusammenfassung |
| The δ18O composition of wetland paleosol siderite spherules is a reliable proxy for
paleoprecipitation δ18O values, a method so far applied to understanding atmospheric
hydrologic conditions during the Albian-Cenomanian (mid-Cretaceous) greenhouse episode.
A new and evolving data set from transects of PETM paleosol locales in North America, with
spot locales from Europe, displays a strong paleolatitudinal gradient. Comparison of the
PETM results to published and new values for the Albian- Cenomanian boundary
suggests that paleoclimatic conditions were very similar during these two greenhouse
episodes. Using the paleosol siderite data as a proxy for paleoprecipitation chemistry,
we benchmark model hindcasts of the Albian-Cenomanian boundary and PETM
episodes using an isotopic tracer model linked to the GENESIS GCM. Model-data
comparisons indicate that our results are robust through the high midlatitudes. Model
results for the high latitudes are sensitive to paleotopographic constraints – only
with geologically realistic paleotopography are we able to adequately model the
paleosol siderite δ18O values in the high latitudes. Suppression of cloud condensation
nuclei, controlled by biological productivity and hypothesized to have occurred
during past episodes of warmth-induced stress on ecosystems, substantially alters
the paleotemperature reconstructions and our modeled paleoprecipitation δ18O
values.
Unpublished δ18O data from siderite concretions obtained from very early Eocene strata,
ODP Leg 189, Site 1171, lie along the paleolatitudinal gradient established from the North
American paleosols. The data, combined with petrographic and major oxide analysis of the
siderite, are suggestive of an episode of enhanced freshwater recharge to the offshore shelf
setting of the Paleogene Tasman Gulf, probably related to elevated precipitation rates
under conditions of an accelerated hydrologic cycle. An anomalous data point in the
PETM paleosol δ18O data from the Yakutat Terrane, southern Alaska, is used to
evaluate potential migration pathways for the terrane – the evaluation suggests that
the Yakutat Terrane is a far-traveled rather than nearby terrane, probably having
originated from near the present Washington-Oregon border, northwestern U.S. |
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