Dominant eukaryotic export production during ocean anoxic events reflects the importance of recycled NH4+
Dominant eukaryotic export production during ocean anoxic events reflects the importance of recycled NH4+
复制标题
DOI：
10.1073/pnas.1104313109
复制
发表时间：
2012-02-14
影响因子：
11.1
通讯作者：
Pearson, Ann
中科院分区：
文献类型：
--
作者：
Higgins, Meytal B.;Robinson, Rebecca S.;Pearson, Ann
The Mesozoic is marked by several widespread occurrences of intense organic matter burial. Sediments from the largest of these events, the Cenomanian-Turonian Oceanic Anoxic Event (OAE 2) are characterized by lower nitrogen isotope ratios than are seen in modern marine settings. It has remained a challenge to describe a nitrogen cycle that could achieve such isotopic depletion. Here we use nitrogen-isotope ratios of porphyrins to show that eukaryotes contributed the quantitative majority of export production throughout OAE 2, whereas cyanobacteria contributed on average approximately 20%. Such data require that any explanation for the OAE nitrogen cycle and its isotopic values be consistent with a eukaryote-dominated ecosystem. Our results agree with models that suggest the OAEs were high-productivity events, supported by vigorous upwelling. Upwelling of anoxic deep waters would have supplied reduced N species (i.e., NH4+) to primary producers. We propose that new production during OAE 2 primarily was driven by direct NH4+-assimilation supplemented by diazotrophy, whereas chemocline denitrification and anammox quantitatively consumed NO3- and NO2-. A marine nitrogen reservoir dominated by NH4+, in combination with known kinetic isotope effects, could lead to eukaryotic biomass depleted in N-15.
