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| Titel |
Biogeochemistry of the North Atlantic during oceanic anoxic event 2: role of changes in ocean circulation and phosphorus input |
| VerfasserIn |
I. Ruvalcaba Baroni, R. P. M. Topper, N. A. G. M. van Helmond, H. Brinkhuis, C. P. Slomp |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 4 ; Nr. 11, no. 4 (2014-02-20), S.977-993 |
| Datensatznummer |
250117236
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| Publikation (Nr.) |
 copernicus.org/bg-11-977-2014.pdf |
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| Zusammenfassung |
The geological record provides evidence for the periodic occurrence of water
column anoxia and formation of organic-rich deposits in the North Atlantic
Ocean during the mid-Cretaceous (hereafter called the proto-North Atlantic). Both
changes in primary productivity and oceanic circulation likely played a role
in the development of the low-oxygen conditions. Several studies suggest that
an increased input of phosphorus from land initiated oceanic anoxic events
(OAEs). Other proposed mechanisms invoke a vigorous upwelling system and an
ocean circulation pattern that acted as a trap for nutrients from the Pacific
Ocean.
Here, we use a detailed biogeochemical box model for the proto-North Atlantic
to analyse under what conditions anoxia could have developed during OAE2 (94 Ma).
The model explicitly describes the coupled water, carbon, oxygen and
phosphorus cycles for the deep basin and continental shelves. In our
simulations, we assume the vigorous water circulation from a recent regional
ocean model study. Our model results for pre-OAE2 and OAE2 conditions are
compared to sediment records of organic carbon and proxies for photic zone
euxinia and bottom water redox conditions (e.g. isorenieratane,
carbon/phosphorus ratios). Our results show that a strongly elevated input of
phosphorus from rivers and the Pacific Ocean relative to pre-OAE2 conditions
is a requirement for the widespread development of low oxygen in the
proto-North Atlantic during OAE2. Moreover, anoxia in the proto-North
Atlantic is shown to be greatly influenced by the oxygen concentration of
Pacific bottom waters. In our model, primary productivity increased
significantly upon the transition from pre-OAE2 to OAE2 conditions. Our model
captures the regional trends in anoxia as deduced from observations, with
euxinia spreading to the northern and eastern shelves but with the most
intense euxinia occurring along the southern coast. However, anoxia in the
central deep basin is difficult to achieve in the model. This suggests that
the ocean circulation used in the model may be too vigorous and/or that
anoxia in the proto-North Atlantic was less widespread than previously
thought. |
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