Rutgers professor sets out to use sound waves to screen images of ancient sea creatures
Gregory Mountain plans to use sound waves to create images of microscopic, ancient sea creatures and the rocks they are embedded in.
Acoustic imaging devices can map the seafloor, creating images and models of the sediments beneath the surface that can help scientists understand how high water levels were millions of years ago, said Mountain, a professor in the Department of Earth and Planetary Sciences.
“We know the water can go in as far as the New Jersey Turnpike and has gone out as far as the continental shelf (in the past),” he said.
Mountain said he plans to create a three-dimensional image of previously mapped terrain in order to better understand it.
The devices work by firing a pellet of air underwater towards the ocean floor, said Kimberly Baldwin, a graduate student in the Department of Earth and Planetary Sciences. A machine called an “airgun” fires a bubble of air toward the ground.
A second pulse is then injected into the bubble to prevent it from collapsing and ensure higher quality sound, Baldwin said.
The sounds recorded by these pulses are at a different frequency than sonar waves, she said. They are more effective at penetrating the ground, which creates a clearer picture than otherwise would be possible.
The device trails behind the ship that the team is attached to, she said. Along with the set of airguns, a group of listening devices are towed by the ship in order to gather data.
The listening devices trail behind the ship to avoid interference from the noise on the vessel itself, such as the ship’s engines, she said.
The sound bounces off different layers of sediments, Mountain said. They can reach up to three-fourths of a mile down, where sediments may be 35 million years old.
Among the actual sediments are tiny fossils that help date the layer, Mountain said.
“We can tell based on the microfossils, the plankton that are in the sediment … if they were in 60 meters of water or 10 meters,” he said.
By understanding how much water these plankton were in when they lived, Mountain said scientists can try to paint a more complete picture of how sea levels rise and fall.
The planet’s temperature is a factor, he said. If the planet is colder, there might be more ice, resulting in lower water levels. When the planet is warmer, the glaciers tend to melt.
“If all the glaciers melted the water would rise 70 meters,” he said. “In the past there has been so much ice the water level was 120 meters lower, (so) that’s the range.”
Some controversy exists over the use of airguns in the ocean. One of the main concerns is that the pulses fired by an airgun harms marine animals, according to Oceana, an organization aimed at protecting marine life.
Oil companies use versions of Mountain’s machine to look for oil, he said. These commercial devices are 10 times larger than the one being used by the scientific team.
More importantly, he said, there are regulations in place that protect marine creatures from harm.
“It’s all overseen by the rule of law,” he said. “They put five marine biologists out on the ship with us, and they are there to enforce the rules. They can tell us to shut down at a moment’s notice, if they perceive any undue harm to marine species.”
These biologists, known as protected species observers, are on constant watch for animals that might be disturbed, he said. The airgun does not necessarily need to actively harm anything for the team to be told to shut down.
Even the slightest disturbance will force a shutdown, he said. If a whale were to stop vocalizing or change the direction it was swimming in because of the expedition’s ship, it would be marked as a "disturbance" or "take." After a certain number of "takes," the crew would be required to stop working altogether.
In a previous expedition the team was shut down briefly to accommodate a group of turtles swimming nearby, Mountain said.
“There’s very little concrete factual data to confirm there is a direct relationship between the seismic sources that we use and any negative impact on the environment,” he said. “I’ve (been doing this) since 1990 (and) have not harmed a marine species (or) angry fisherman.”
Another complaint is that the ship’s presence might scare away fish and other marine animals in the region, Mountain said. Based on his previous experiences, Mountain said he does not think this is likely.
Mountain said he saw several creatures in his previous trips that would not be there if they were scared away.
“We were out last summer, (and) the protected species observers saw two whales,” he said. “You can’t say we scared them all off, because we’re shooting all the time.”
Mountain said this is the first year he received any backlash on using airguns.
It would be important for skeptics to understand how the technology works and what regulations are in place to protect ocean life, he said.
The goal of the research is to help protect human lives through understanding sea level change, he said.
“One-hundred million human beings live (so) close to sea level in elevation, (that) the height the sea level is going to rise over the next 100 years (will impact them),” he said.