Global monsoon drives long-term carbon cycles in the ocean

Physorg: For over 300 years, monsoon has been considered as a gigantic land-sea breeze of regional scale, but now it is considered as a global system over all continents but Antarctica. This new develoment in modern climatology, however, has not yet been responded by paleo-climatology.

Prof. Pinxian Wang from Tongji University, Shanghai, reviews the geological evolution of the global monsoon and its impact, showing that the global monsoon exists through all geological history since at least 600 million years ago. It covaries with various geological cycles including those caused by the geometric changes of the Earth's orbits. The 20,000-year precessional cycle of the global monsoon, for example, is responsible for the collapse of several Asian and African ancient cultures at ~ 4000 years ago. The same cyclicity is seen in the chemical composition of the air, such as methane concentration and isotope composition of air-bubbles captured in ice cores.

Now Wang found that the long-term cycles in the oceanic carbon reservoir also has a global monsoon origin. This 400,000-year cyclicity related to "long eccentricity" of the Earth's orbit, is best seen in carbon isotope compositions of calcite test of foraminifera, a single-cell animal in the ocean. The rhythmic changes in oceanic carbon reservoir were likened to "heartbeat" of the Earth system. This cyclicity becomes longer since 1.6 million years ago, displaying a kind of "arrhythmia" in the Earth system, probably resulting from the growth of the Arctic ice. Although the mechanism of how monsoon drives oceanic carbon cycle remains unclear, the monsoon-related long-term cyclicity should not be overlooked in carbon-cycle modeling for long-term climate prediction….

Monsoon in Manipur, shot by Mongyamba, Wikimedia Commons, under the Creative Commons Attribution ShareAlike 3.0 License.