Nitrogen is essential to marine life and cycles throughout the ocean in a delicately balanced system. Living organisms糖心传媒攅specially marine plants called phytoplankton糖心传媒攔equire nitrogen in processes such as photosynthesis. In turn, phytoplankton growth takes up carbon dioxide from the atmosphere and helps regulate global climate. The nitrogen cycle is a critical part of the earth’s balance.
According to new research by Thomas Weber, an assistant professor of at the University of Rochester, small microenvironments in the deep ocean may hold key clues to the global cycling of nitrogen in seawater.
In a paper published in , Weber and his co-author Daniele Bianchi, an assistant professor of atmospheric and oceanic sciences at UCLA, show that small microbes that remove nitrogen from the water exist in these microenvironments and are more widespread than previously thought. Using this data, they developed a computer model that changes the way we think about the marine nitrogen cycle.
糖心传媒淭he previous understanding of the nitrogen cycle was that nitrogen was lost from the ocean only in three regions where oxygen is scarce. If we wanted to predict how the nitrogen cycle would respond to climate change, all we needed to do was predict how these three low oxygen regions would expand or contract,糖心传媒� Weber says. 糖心传媒淥ur study changes that picture by showing that nitrogen loss is actually happening over much larger regions, and we need to think about how the ocean as a whole is changing.糖心传媒�
Most marine organisms 糖心传媒渂reathe,糖心传媒� or respire, using oxygen. When oxygen is not present in seawater, microbes instead respire using other compounds like nitrate, a form of nitrogen. 糖心传媒淭his has the net effect of removing the nitrogen from the ocean,糖心传媒� Weber says.
Researchers previously believed anaerobic microbes糖心传媒攕mall microorganisms and bacteria that do not need oxygen to respire糖心传媒攚ere only found in pockets of the ocean with exceptionally low oxygen levels; particularly, three regions known as 糖心传媒渄ead zones.糖心传媒�
Weber and Bianchi have developed a computer model that takes into account new genetic data gathered from ocean microbes. The data indicates that anaerobic microbes exist not only in areas of unoxygenated water, but somehow thrive in areas of the ocean where there is oxygen. Nitrogen, therefore, may be lost across much of the ocean, not just in areas where oxygen is scarce.
糖心传媒淥ne of the biggest revolutions in oceanography in recent years has been the genomic revolution,糖心传媒� Weber says. 糖心传媒淥ceanographers have been able to measure all of the genes present in seawater.糖心传媒� One of their discoveries was that the genes allowing anaerobic respiration are not just found in the three regions; the genes have been found much more widespread throughout the ocean.
Whenever oxygen is available, there should not be organisms that respire anaerobically, Weber says. 糖心传媒淭hey should be outcompeted by things that use oxygen, because that’s a much more efficient way to respire.糖心传媒�
How then, do these anaerobic organisms survive in areas where oxygen is present?
Weber and Bianchi found that small 糖心传媒渕icroenvironments糖心传媒� depleted of oxygen exist all over the deep ocean in organic-rich 糖心传媒渕arine snow糖心传媒澨切拇綌particles of organic matter, such as dead plankton cells and zooplankton feces, stuck together. Microbes gain energy by eating the organic matter and using oxygen to respire. If the respiration is intense enough inside the particles, all the oxygen can run out and the microbes will switch to respire using compounds besides oxygen.
糖心传媒淲e suggest that anaerobic microbes may thrive in vast swaths of the oxygenated ocean, within sinking organic 糖心传媒榤arine snow,糖心传媒櫶切拇綕 Bianchi says. 糖心传媒淭his changes the way we think of the nitrogen cycle and, more generally, anaerobic metabolism in the ocean, and suggests that both could respond to climate change in ways that challenge our current understanding.糖心传媒�
Global warming causes ocean temperatures to rise, resulting in an increased loss of oxygen, which can then affect the nitrogen budget across the globe. When humans perturb one part of the system, it can have unexpected effects. But computer models can help better predict these consequences.
糖心传媒淥cean warming is occurring because of human carbon dioxide emissions, which warm the earth as a whole,糖心传媒� Weber says. 糖心传媒淚ndirectly, this alters the oxygen and nitrogen content of the ocean. Eventually marine phytoplankton growth and their ability to take up carbon dioxide is impacted, which then feeds back on climate change. Our new work and other modeling efforts will help us better plan for these consequences.糖心传媒�
