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1.
Nature ; 459(7250): 1114-7, 2009 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-19553996

RESUMO

The modern Eastern Equatorial Pacific (EEP) Ocean is a large oceanic source of carbon to the atmosphere. Primary productivity over large areas of the EEP is limited by silicic acid and iron availability, and because of this constraint the organic carbon export to the deep ocean is unable to compensate for the outgassing of carbon dioxide that occurs through upwelling of deep waters. It has been suggested that the delivery of dust-borne iron to the glacial ocean could have increased primary productivity and enhanced deep-sea carbon export in this region, lowering atmospheric carbon dioxide concentrations during glacial periods. Such a role for the EEP is supported by higher organic carbon burial rates documented in underlying glacial sediments, but lower opal accumulation rates cast doubts on the importance of the EEP as an oceanic region for significant glacial carbon dioxide drawdown. Here we present a new silicon isotope record that suggests the paradoxical decline in opal accumulation rate in the glacial EEP results from a decrease in the silicon to carbon uptake ratio of diatoms under conditions of increased iron availability from enhanced dust input. Consequently, our study supports the idea of an invigorated biological pump in this region during the last glacial period that could have contributed to glacial carbon dioxide drawdown. Additionally, using evidence from silicon and nitrogen isotope changes, we infer that, in contrast to the modern situation, the biological productivity in this region is not constrained by the availability of iron, silicon and nitrogen during the glacial period. We hypothesize that an invigorated biological carbon dioxide pump constrained perhaps only by phosphorus limitation was a more common occurrence in low-latitude areas of the glacial ocean.


Assuntos
Carbono/metabolismo , Carbono/química , Diatomáceas/metabolismo , Sedimentos Geológicos/química , Oceano Pacífico , Silício/análise , Fatores de Tempo
2.
Science ; 320(5878): 893-7, 2008 May 16.
Artigo em Inglês | MEDLINE | ID: mdl-18487184

RESUMO

Increasing quantities of atmospheric anthropogenic fixed nitrogen entering the open ocean could account for up to about a third of the ocean's external (nonrecycled) nitrogen supply and up to approximately 3% of the annual new marine biological production, approximately 0.3 petagram of carbon per year. This input could account for the production of up to approximately 1.6 teragrams of nitrous oxide (N2O) per year. Although approximately 10% of the ocean's drawdown of atmospheric anthropogenic carbon dioxide may result from this atmospheric nitrogen fertilization, leading to a decrease in radiative forcing, up to about two-thirds of this amount may be offset by the increase in N2O emissions. The effects of increasing atmospheric nitrogen deposition are expected to continue to grow in the future.


Assuntos
Atmosfera , Atividades Humanas , Nitrogênio , Espécies Reativas de Nitrogênio , Água do Mar , Carbono , Dióxido de Carbono/metabolismo , Ecossistema , Humanos , Nitrogênio/metabolismo , Fixação de Nitrogênio , Oceanos e Mares , Espécies Reativas de Nitrogênio/metabolismo
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