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| Titel |
A regional ocean circulation model for the mid-Cretaceous proto-North Atlantic Basin: implications for black shale formation |
| VerfasserIn |
Robin Topper, João Trabucho Alexandre, Erik Tuenter, Paul Meijer |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036385
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| Zusammenfassung |
| In the Mesozoic, high amounts of organic matter accumulated in marine sediments during
Oceanic Anoxic Events (OAEs). OAEs are stratigraphic intervals defined by δ13C excursions,
which are thought to be the result of perturbations in the global carbon cycle. Whether the
local lithological expression of an OAE is organic-rich or not, depends on palaeogeography
and local climate.
Model studies of these events invariably make use of global ocean circulation models.
In this study, however, a regional model for the proto-North Atlantic Basin at the
Cenomanian-Turonian boundary is developed and tested. Advantages of a regional model
over a global model are a higher resolution (0.5- x 0.5 -) and shorter model run times
allowing for more sensitivity experiments. A version of MOMA was adapted for application
to the mid-Cretaceous proto-North Atlantic Basin. Surface boundary conditions (virtual salt
flux and heat flux) are extracted from the results of a recent global Cenomanian
CCSM3 run. The bathymetry represents the proto-North Atlantic Basin at ca. 90 Ma
and is constructed from the oceanic lithosphere reconstruction from Müller et al.
(Science, 319, 1357-1362, 2008) and the bathymetry from Sewall et al. (Clim. Past, 3,
647-657, 2007). A first-order check of the results is performed by comparison with the
results from the global Cenomanian CCSM3 run. The regional model proves to be
able to maintain tracer patterns and produce velocity patterns similar to the global
model.
In order to test the hypothesis that ocean circulation may be behind the deposition of
black shales during OAEs, the regional model was used to examine changes in the
proto-North Atlantic circulation for three different sets of boundary conditions, which are
interpreted as representing scenarios for pre-OAE, OAE and post-OAE time envelopes. The
pre-OAE scenario has a 150 metre lower sea level with respect to the OAE scenario which
results in a decrease in continental shelf area, influencing both deep water formation and
upwelling along the coasts. In the post-OAE scenario a deep water connection with the South
Atlantic Ocean is implemented and it results in a change in the source for proto-North
Atlantic intermediate water and hence in the source for water which replenishes
upwelling along the South American and African coast. We will discuss (changes in) the
circulation and upwelling patterns and (anticipated) nutrient supply for all three
scenarios to predict whether and where the conditions in the proto-North Atlantic
were favourable for black shale formation during each of these time envelopes. |
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