MadSci Network: Environment & Ecology

Re: What happens to the (iron) in Oceans because of (Ultravalet) light?

Date: Thu Dec 10 15:13:46 1998
Posted By: Karen Culver-Rymsza, Biological Oceanographer
Area of science: Environment & Ecology
ID: 912200496.En

Dear Richard,

The ocean waters around Antarctica are interesting in many ways. This is a very dynamic area of ocean and has been the subject of much research. The iron issue is not so much a case of sinking iron as it is an illustration of the way global biogeochemical cycles affect life.

The topic you touched on is known as "The Iron Hypothesis". It was described by the late John Martin of Moss Landing Marine Lab in California. There is a long history of interest in iron in the sea, but Martin was able to demonstrate his hypothesis.

What Martin did was look at an area of the ocean around Antarctica that is known to have high levels of dissolved nitrogen. Nitrogen is the mineral that limits phytoplankton growth in most of the ocean. Here there was excess nitrogen, but not a lot of phytoplankton. This means of course that something else was limiting the growth of phytoplankton there. Knowing the biogeochemistry of iron made it a likely candidate. You see, most iron enters the sea from river runoff but this doesn't reach far beyond coastal waters. At great distances from land the major source of iron is wind blown terrigenous (from land) material. This can be seen in higher iron concentrations at latitudes that correspond to large deserts -- a major source for windblown dust. Antarctica has neither large amounts of runoff nor much windblown transport due to its ice cap.

Unfortunately Martin died before he had the opportunity to test his hypothesis, but there is data to support it. Iron added to seawater containing phytoplankton does ‘grow' more than without. There was a large scale iron fertilization experiment in the Pacific that further supports the hypothesis. Iron has a low solubility in seawater., so in the IronEx experiment, the added iron eventually came out of solution and sank. and the growth rates of the algae returned to normal.

There is quite a bit of information on this topic available. I have included a couple of websites for more information.

The National Science Foundation's Press Release
"The Geritol Effect"

As for the ozone hole part of your question... UV causes damage to DNA to marine life as well as people. The added UV light that reaches the Southern Ocean does affect the flora and fauna there, but as far as I know there is no direct relationship between iron and UV light. UV light can affect organic compunds, some of which may affect the solubility of iron.

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