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Medientyp:
E-Artikel
Titel:
Dynamic model constraints on oxygen-17 depletion in atmospheric O 2 after a snowball Earth
Beteiligte:
Cao, Xiaobin;
Bao, Huiming
Erschienen:
Proceedings of the National Academy of Sciences, 2013
Erschienen in:
Proceedings of the National Academy of Sciences, 110 (2013) 36, Seite 14546-14550
Sprache:
Englisch
DOI:
10.1073/pnas.1302972110
ISSN:
0027-8424;
1091-6490
Entstehung:
Anmerkungen:
Beschreibung:
A large perturbation in atmospheric CO 2 and O 2 or bioproductivity will result in a drastic pulse of 17 O change in atmospheric O 2 , as seen in the Marinoan Oxygen-17 Depletion (MOSD) event in the immediate aftermath of a global deglaciation 635 Mya. The exact nature of the perturbation, however, is debated. Here we constructed a coupled, four-box, and quick-response biosphere–atmosphere model to examine both the steady state and dynamics of the MOSD event. Our model shows that the ultra-high CO 2 concentrations proposed by the “snowball’ Earth hypothesis produce a typical MOSD duration of less than 10 6 y and a magnitude of 17 O depletion reaching approximately −35‰. Both numbers are in remarkable agreement with geological constraints from South China and Svalbard. Moderate CO 2 and low O 2 concentration (e.g., 3,200 parts per million by volume and 0.01 bar, respectively) could produce distinct sulfate 17 O depletion only if postglacial marine bioproductivity was impossibly low. Our dynamic model also suggests that a snowball in which the ocean is isolated from the atmosphere by a continuous ice cover may be distinguished from one in which cracks in the ice permit ocean–atmosphere exchange only if partial pressure of atmospheric O 2 is larger than 0.02 bar during the snowball period and records of weathering-derived sulfate are available for the very first few tens of thousands of years after the onset of the meltdown. In any case, a snowball Earth is a precondition for the observed MOSD event.