Iron is present in tiny concentrations in seawater. On the order of a few billionths of a gram in a liter.
"I did a calculation once on a ton of ocean water," says Seth John, an assistant professor in the department of marine science at the University of South Carolina. "The amount of iron in that ton of water would weigh about as much as a single eyelash."
Given that there is so little iron in seawater, one might conclude that its presence there is inconsequential.
Hardly. Iron is one of the essential elements of life. Found in enzymes like myoglobin and hemoglobin and cytochrome P450, iron is an essential cog in the biomachinery of every living cell. And its scarcity in the ocean, the earth's wellspring of life, only magnifies its importance.
"The key reason that everybody cares about iron is because it limits the growth of phytoplankton, such as algae, in maybe a fifth of the ocean," says John, a researcher in the School of Earth, Ocean and Environment in South Carolina's College of Arts and Sciences.
In those iron-poor places, there's plenty of everything else that phytoplankton, the base of the food web, need to grow sunlight, carbon, fixed nitrogen, water. Just a small change in the amount of iron that finds its way there can have a dramatic impact on the growth of photosynthetic organisms and their concomitant uptake of carbon dioxide.
When algae and other phytoplankton grow, they take carbon dioxide out of the atmosphere, converting it into proteins and other carbon-based molecules that constitute living cells. And it takes very little iron to keep this process going in a typical cell, for every atom of iron, there are about a million atoms of carbon, says John. A little iron goes a long way in allowing phytoplankton to grow and pull carbon dioxide out of the air.
Knowing how iron moves into the oceans is thus crucial for scientists to fully understand the details of the carbon cycle on ea
|Contact: Steven Powell|
University of South Carolina