Thousands of years ago, the Earth was going through an ice age and conditions were harsh: it was much colder and windier compared to today, and large amounts of dust were being scattered in the air and much of it contained iron. The iron eventually found its way into the oceans and many scientists believe that the extra iron increased the growth of tiny forms of marine life. One part of the puzzle of iron fertilization of the oceans has been evaluated by an international team of researchers that includes a Texas A&M University scientist.
Franco Marcantonio, a professor in the Department of Geology and Geophysics at Texas A&M, and colleagues from Columbia University, Princeton, the University of California-Santa Cruz and the National Taiwan University have the results of their work published in the current issue of Nature magazine.
By analyzing core samples taken from deep waters of the central Pacific Ocean, the researchers discovered that there was increased dust-containing iron settling into the oceans during the last ice age.
But were there sufficient amounts of iron to help fertilize the surface waters so that carbon dioxide could be drawn out of the atmosphere? It is an important question because it goes to the heart of what causes warm-cold cycles on Earth, the researchers believe.
“All of this dust contained iron, which is an important nutrient for ocean phytoplankton growth,” explains Marcantonio.
He adds that even though there were larger amounts of iron being delivered to the equatorial Pacific Ocean during the last ice age, it was not enough to cause fertilization of this huge region.
“That means that something else has to account for the decrease of carbon dioxide in the atmosphere that contributed to making the Earth colder during the last ice age,” he points out.
“This decrease of carbon dioxide during cold times is probably related to what was going on in the high-latitude oceans of the southern hemisphere.
“We found that although there was more delivery of iron to the equatorial Pacific Ocean during the last ice age – 17,000 to 27,000 years ago – there was not an increase in the growth of phytoplankton, which is the opposite of what has been recently proposed by other scientists.
“We think the reason productivity did not increase is because the amount of nutrients were reduced in the deep water being brought up to the surface.”
Marcantonio says this process of upwelling, where cold ocean waters rich in nutrients rise up to the surface from the deep, usually leads to increased productivity of organisms at the surface.
The study was funded by the National Science Foundation.
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