Microscopic algae (phytoplankton) make a living in the same way as land plants, by photosynthesis using the sunlight that penetrates the upper 100 meters. They take the building blocks for their cells, which are carbon, nitrogen, phosphorous and trace elements, like the metals iron or zinc, from the surrounding water.
When these algae die, they fall into the dark deep ocean, where their cells are degraded by bacteria. The trace elements are now far away from the region where other organisms would need them. So far, geochemists believed, that they are lost forever to phytoplankton on the ocean surface.
The journey of trace elements in the ocean
The rate, at which phytoplankton removes carbon dioxide from the surface water, depends on the availability of the nutrients. So, how
these elements are removed from the upper ocean and recycled back there from the deep is crucial for how the past, current and future climate of the Earth operates.
In a recent study, researchers from ETH Zurich, led by geochemist Derek Vance, have used ocean chemistry tracers to reveal that a significant portion of many metals is rapidly and permanently removed from seawater—not by biological processes, but by becoming incorporated into solid manganese-oxide particles. These particles precipitate out of seawater and sink all the way to the ocean floor, where they become part of the sediment.
However, the team also found that chemical reactions within the sediment can release these metals from the solid manganese oxide, returning them to the deepest layers of seawater. Using a numerical model to simulate ocean transport processes, the researchers demonstrated that metals released in this way can leak from the sediment back into the deep ocean, where they are then mixed and circulated throughout the ocean once again.
Read the full paper.
