Publication Date:
2019
Description:
〈p〉The million-year variability of the marine nitrogen cycle is poorly understood. Before 57 million years (Ma) ago, the 〈sup〉15〈/sup〉N/〈sup〉14〈/sup〉N ratio (〈sup〉15〈/sup〉N) of foraminifera shell-bound organic matter from three sediment cores was high, indicating expanded water column suboxia and denitrification. Between 57 and 50 Ma ago, 〈sup〉15〈/sup〉N declined by 13 to 16 per mil in the North Pacific and by 3 to 8 per mil in the Atlantic. The decline preceded global cooling and appears to have coincided with the early stages of the Asia-India collision. Warm, salty intermediate-depth water forming along the Tethys Sea margins may have caused the expanded suboxia, ending with the collision. From 50 to 35 Ma ago, 〈sup〉15〈/sup〉N was lower than modern values, suggesting widespread sedimentary denitrification on broad continental shelves. 〈sup〉15〈/sup〉N rose at 35 Ma ago, as ice sheets grew, sea level fell, and continental shelves narrowed.〈/p〉
Print ISSN:
0036-8075
Electronic ISSN:
1095-9203
Topics:
Biology
,
Chemistry and Pharmacology
,
Computer Science
,
Medicine
,
Natural Sciences in General
,
Physics
Permalink