Alteration of Ocean Chemistry by Small Migrating Marine Animals
A recent study by the researchers of the University of Washington claims that regular migration helps change shape oceans. In presence of daylight the animals residing there release ammonia, the equivalent of urine, which plays a significant role in marine chemistry, specifically in oxygen deprived zones.
The largest migration on the planet is the journey of small animals from the surface of the open ocean, where they feed on plants under cover of darkness, to the sunless depths where they hide from predators during the day.
It is really surprising to think that urination could change the ocean chemistry, considering the vastness of the oceans compared to the volume of the urine. But the animals: tiny zooplankton, crustaceans and fish such as lantern-fish are huge in abundance. Thus their cumulative effect is responsible for the change in ocean chemistry.
After night time meal close to the surface, these small creatures take a couple of hours to swim about 650 to 2,000 feet (200 to 600 meters) deep. Solid waste falls as pellets. The liquid waste is emitted more gradually.
An earlier study reported that the animals spend almost the whole day in low-oxygen water. Marine bacteria consume oxygen as they decompose sinking dead material, creating low-oxygen zones a few hundred feet below the surface. These animals actually contribute to these low-oxygen zones by using the little remaining oxygen to breathe.
In the recent study, data was collected from underwater sonar surveys to calculate how many animals are migrating to which depths, and where. Next they gauged the combined effect of their daytime digestion. Results show that in certain parts of the ocean, ammonia released from animals drives a big part of the oxygen-free conversion of ammonium and other molecules to nitrogen gas, a key chemical transition.
Though bacteria were solely blamed for this job, yet the effect of animals is not negligible to alter the rates of these reactions. The mechanism of conversion of ammonia to a pair of nitrogen atoms, by bacteria is still uncertain. Yet the conversion is important because it determines how much nitrogen-based fertilizer remains to support life in the oceans.
The ocean’s low-oxygen zones are projected to expand under climate change, as warmer waters hold less oxygen and decrease oxygen content below the surface. Understanding these zones is thus important for predicting what might happen to the oceans under climate change.
D. Bianchi, A. R. Babbin, E. D. Galbraith. Enhancement of anammox by the excretion of diel vertical migrators. Proceedings of the National Academy of Sciences, 2014; DOI: 10.1073/pnas.1410790111
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