Climate Fact: Nitrogen Flows in Ancient Seas
Excessive nitrogen concentrations in ocean water can cause so much life to bloom that oxygen supplies are depleted and “dead zones” form. But without nitrogen, no life is possible and generally, the more available nitrogen there is, the more life there will be. When plankton (tiny organisms that ultimately feed all other life in the ocean) have completed their life-cycles, their bodies fall to the ocean floor and become part of the geologic record. These bodies record relative isotope concentrations (the concentrations of atoms of the same element, but with different atomic masses), including the proportions of nitrogen 14 and nitrogen 15. The proportion of nitrogen 14 to nitrogen 15 found in these bodies can be used to determine how much nitrogen the oceans were”fixing,” or taking out of the atmosphere. When more nitrogen is coming into the seas, the proportion of nitrogen 14 to nitrogen 15 increases. Analysis of sediment samples from about 30,000 years ago to the present demonstrate that during the last ice age (which ended about 10,000 years ago), the oceans were taking up only about 20 percent of the amount of nitrogen that they are today. The amount of denitrification, or the out-gassing of nitrogen from oceans to the atmosphere, that happened then was also much lower, which suggests that over long periods of time (hundreds to thousands of years), ocean ecosystems adapt to keep nitrogen inputs and outputs in balance.
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Source: Montoya, JP. “Old New Nitrogen.” Science 323 (2009): 219-220.
