Researchers at the USF College of Marine Science in St. Petersburg received a $907,000 grant from the National Aeronautics and Space Administration to test a hypothesis that examines the distribution of carbon molecules in the world’s oceans, particularly near continental shelves.
This research could have implications on the role that carbon molecules play in global warming, said Frank Muller-Karger, a professor in the College of Marine Science and founder of USF’s Institute for Marine Remote Sensing.
“One of the big questions in oceanography is how much carbon dioxide goes into the water and what are the processes that impact how much stays in the water, and how much goes and sinks to the bottom?” Muller-Karger asked.
The reason USF researchers are specifically looking at continental shelves in relation to the distribution of carbon dioxide in the water is because the continental shelves have been overlooked in every model used to determine the amount of carbon dioxide in the water, Muller-Karger said. According to his hypothesis, these shelves may be playing a bigger part than once thought in helping to diminish global warming.
Continental shelves are the parts of land that continue under the ocean until the depth reaches about 600 feet. At that depth, the land typically drops off into deep waters, Muller-Karger said. The continental margin, which Muller-Karger is most concerned with, consists of the continental shelf as well as the slope that begins when the land falls away to deeper depths.
According to Muller-Karger’s hypothesis, carbon dioxide molecules that enter the water may not leave. Some of them may be getting trapped at the bottom of the ocean, buried under sediment and removed from the atmosphere.
The way this works, Muller-Karger said, is that carbon molecules in the atmosphere can enter the ocean when there is a lower concentration of them in the water.
“That’s just the way molecules work, they tend to go from high concentrations to low concentrations by a process called diffusion. They keep moving until there is an equilibrium,” he said.
Once the carbon molecules enter the water, they can be taken in by microscopic marine plant life known as phytoplankton. These phytoplankton use the carbon through a process of photosynthesis in which the plant takes in carbon dioxide and uses sunlight to produce food. Fish and other marine life then come along and eat these plants. After dying or being eaten, some end up falling to the bottom of the ocean floor, past the continental margins. It is believed, based on Muller-Karger’s hypothesis, that the carbon molecules reaching the bottom of the ocean are buried by other molecules or sediments.
“The reason that it is interesting to look at the stuff that reaches the bottom is that if it becomes buried there then you have effectively removed carbon dioxide from the atmosphere and buried it for a thousand years if not millions of years,” Muller-Karger said.
Because carbon molecules are removed from the ocean when eaten by fish or falling to the ocean floor, the concentration of carbon molecules in the water decreases. This will cause carbon molecules to migrate into the water if the atmosphere has a higher concentration, Muller-Karger said. He calls this a “natural pump.”
“Many people are trying to understand how this happens on a global level. If we put so many tons of carbon dioxide in the atmosphere by burning fuels, forests and so on, how much goes into the ocean, land and atmosphere? It is a very important question,” Muller-Karger said.
Agencies, such as the Oceanic and Atmospheric Administration and Princeton University, are currently measuring the concentration of carbon molecules in the ocean using numerical computer models that simulate what happens in the world, Muller-Karger said. These computer models use a grid, which contains a number of squares. The grid is overlaid onto a globe and each square within the grid typically represents 60 miles of the surface of the earth.
“The problem with these models is the spatial resolution. Basically, each one of the squares is pretty big. If you bunched everything up that you have around you, including you, in a 60 square mile radius and gave it one number, it would be a pretty crude approximation of what the world is,” Muller-Karger said.
Due to the use of these models, important areas such as the continental margins are overlooked and considered to have the same amount of carbon in them as the rest of the ocean. This may not be true if Muller-Karger’s hypothesis proves to be true.
Muller-Karger’s model uses satellite photographs, which take actual pictures of the surface of the ocean. His model is based on a matrix of squares in which each square only represents one to five miles.
“I can actually see what is happening because the satellite actually sees what’s going on. It is not just a simulation, it is an actual measurement,” Muller-Karger said.
In his model Muller-Karger overlays the satellite photos over a globe, which shows the actual depths of the ocean at different locations. The satellite photographs also show the amount of plants that grow near the surface of the water. They are seen in the photographs because they change the color of the water Muller-Karger said.
If his hypothesis is correct, it will mean that all the models to date attempting to explain where greenhouse gasses are going are wrong. But this model might also help devise a way in which the world can slow down the build up of greenhouse gasses in the atmosphere.