Around the world, wide swaths of open ocean are nearly depleted of oxygen. Not quite dead zones, they are “oxygen minimum zones,” where a confluence of natural processes has led to extremely low concentrations of oxygen. Only the hardiest of organisms can survive in such severe conditions, and now MIT oceanographers have found that these tough little life-forms — mostly bacteria — have a surprisingly low limit to the amount of oxygen they need to breathe. In a paper published online on November 25, 2016 by the journal Limnology and Oceanography, the team reports that ocean bacteria can survive on oxygen concentrations as low as approximately 1 nanomolar per liter. To put this in perspective, that’s about 1/10,000th the minimum amount of oxygen that most small fish can tolerate and about 1/1,000th the level that scientists previously suspected for marine bacteria. The researchers have found that below this critical limit, microbes either die off or switch to less common, anaerobic forms of respiration, taking up nitrogen instead of oxygen to breathe. The open-access artice is titled “A Theoretical Basis for a Nanomolar Critical Oxygen Concentration.” With climate change, the oceans are projected to undergo a widespread loss of oxygen, potentially increasing the spread of oxygen minimum zones around the world. The MIT team says that knowing the minimum oxygen requirements for ocean bacteria can help scientists better predict how future deoxygenation will change the ocean’s balance of nutrients and the marine ecosystems that depend on them.
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