Understanding Climate Dynamics at USC: Nitrogen Fixation in the World Ocean

As concerns over climate change increase, it is important for scientists to understand the cycles of Earth’s natural systems and elements. For example, one-third of the carbon dioxide in the atmosphere, including that from anthropogenic sources, is taken up by the ocean.  As a result, marine environments are an important part of the carbon cycle and climate research.

On the ocean’s surface, marine phytoplankton (photosynthetic organisms such as plants and algae) take up carbon dioxide and nitrogen to make organic material. Once they die and sink to the bottom, the phytoplankton carry that carbon and nitrogen with them to the deep. This provides a benefit to the planet, by removing carbon from the atmosphere and storing it on the bottom of the ocean for centuries.

Although carbon is relatively abundant, there is only so much usable nitrogen in the upper ocean to support phytoplankton growth and aid in this important process. This makes marine nitrogen a “limiting” component controlling the rate at which oceans can reduce Earth’s atmospheric carbon dioxide levels. Until just a decade ago, scientists were unclear about where marine nitrogen came from, making it difficult to study these dynamics.

But in recent years, researchers with the USC Wrigley Institute have discovered an important source of nitrogen.  Marine bacteria in the upper ocean, such as the cyanobacterium Trichodesmium, take nitrogen gas from the air and convert it into usable forms for marine life. Such bacteria were never considered important contributors to upper ocean environments. By surveying various regions of the world ocean, Wrigley scientists found that these bacteria are actually a prominent part of ocean ecosystems. As a result, scientists worldwide now have a new paradigm for understanding nitrogen in the ocean – and thus a better understanding of the ocean’s capability for absorbing carbon into the deep, potentially mitigating carbon dioxide in the atmosphere and climate changes on the Earth as a whole.


Affiliated Faculty:
Doug Capone