The Global Nitrogen Budget and the Faint Young Sun Paradox

Details The Global Nitrogen Budget and the Faint Young Sun Paradox The Global Nitrogen Budget and the Faint Young Sun Paradox

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p33d..02g&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P33D-02

Physics

0325 Evolution Of The Atmosphere (1610, 8125), 0343 Planetary Atmospheres (5210, 5405, 5704), 0469 Nitrogen Cycling, 5225 Early Environment Of Earth, 5405 Atmospheres (0343, 1060)

Scientific paper

Models of the early Earth Climate invariably assume that the Archean atmospheric nitrogen inventory was equal to today's, or that Archean atmospheric pressure was 1 bar. Here, we relax this assumption and present radiative-convective climate model results for the late Archean atmosphere with 0.5, 1, 2 and 3 times the present atmospheric nitrogen inventory and varying carbon dioxide concentrations. Nitrogen is taken to be radiatively inert, but an increased nitrogen inventory causes a surface warming by pressure broadening of the adsorption bands of radiatively active species and through a pressure-lapse rate feedback. Assuming 25 times present carbon dioxide mixing ratio at 2.8 Ga, twice the present nitrogen inventory would give an 11K warming compared to the present nitrogen inventory, yielding a surface pressure of 286K. Thus it provides a possible solution to the Faint Young Sun paradox. Conversely, if the nitrogen inventory of the early atmosphere had been less, modeled surface temperature would be much colder and the Faint Young Sun paradox would be much more difficult to solve. The present atmospheric nitrogen inventory is 3.9 × 1018 kg N. Venus has three times this amount in its atmosphere, which suggests that Earth may have had more nitrogen than is currently obvious. The continental crust contains 1-2× 1018 kg N, which would have accumulated with continental growth, thought to have happened mostly since ~ 2.7 Ga. A larger hidden nitrogen reservoir may exist in the mantle. The present rate of transfer of nitrogen from the ocean crust and sediments to the mantle (subduction minus volcanism) has been reported to be ~ 7.5 × 108 kg yr-1, at which rate ~ 2 × 1018 kg N would have been transferred to the mantle since 2.7 Ga. Subduction rates in the past may well have been higher, so this may represent a lower bound. Thus twice the present atmospheric nitrogen inventory in the late Archean is a plausible estimate.

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