Researchers from Princeton University and the Swiss Institute of Technology in Zurich (ETH) said that during the past 160,000 years nitrogen fixation rose and fell in a pattern that closely matched the changing orientation of Earth's axis of rotation, or axial precession.
Axial precession occurs on a cycle of roughly 26,000 years and arises because the Earth wobbles slightly as it rotates, similar to the wobble of a toy top.
Second author Daniel Sigman, Princeton's Dusenbury Professor of Geological and Geophysical Sciences, said that the finding that nitrogen fixation is determined by precession-driven upwelling appears to indicate that the ocean's fixed nitrogen reservoir is resilient and that the ocean biosphere can recover from even the most dramatic ecological changes.
The researchers tracked changes in nitrogen fixation in the North Atlantic Ocean by measuring the fixed nitrogen contained in the shells of marine animals recovered from sediment in the Caribbean Sea.
Working in Sigman's lab, the investigators measured the amount of two types of nitrogen known as 14N and 15N contained in the shells of tiny marine animal plankton called foraminifera. The ratio of 15N to 14N was then used to reconstruct the rate of nitrogen fixation.
The pattern of nitrogen fixation measured in foraminifera matched the historical record of axial precession and the resulting ocean upwelling.
The new study has been published in the journal Nature.
--ANI (Posted on 14-09-2013)