"Dead Zones," areas in the ocean that contain so little oxygen that life cannot exist, have created a serious ecological horror. Even more troubling, these dead zones are expanding.
Dead zones can occur naturally from time to time along coasts, forcing animals to flee the area or die. However, due to human impact, dead zones are both increasing in size and number, with 400 cited dead zones worldwide. This count is doubling every decade with no sign of slowing down.
Most dead zones are formed near coastal waters where rivers dump loads of waste into the ocean. However, these zones have recently been discovered in open ocean waters, such as in the Pacific northwest.
Scientists believe that these open ocean dead zones are a direct result of human impact as well, not through the dumping of waste, but a long-term consequence of human activities on on the climate.
First found in 2002 by scientists, dead zones are becoming more and more prominent.
By 2004, ordinary people living near coastal waters were beginning to take note of them. Photos emerged of people standing knee-deep in piles of dead crabs that the coastal tide had washed up on the beach.
In 2006, researchers at Oregon State University observed oxygen levels at zero for the first time. The researchers saw the effects of the drop in oxygen. There were no fish, piles of dead marine life on the sea floor and dead worms floating in the current.
All of these findings begged the question: What is causing these dead zones to expand?
Realizing that they would need a broad continuous view under the sea surface, the scientists at Oregon State constructed underwater robotic gliders to try and find an answer.
These robotic gliders were capable of venturing under the ocean's surface for up to three weeks on their own and provided real time data on the "pulse" of the ocean every six hours. The gliders were far more technologically advanced than previous tools used to view the state of the ocean.
They were capable of maneuvering through the infamous rough waters of Oregon's coast. Equipped with a GPS and a steering mechanism, the robotic gliders could avoid obstacles underwater (through the use of sonar) and therefore, did not have to be controlled or monitored by researchers.
The robotic gliders had other advantages: they did not get seasick or tired. As trivial as this statement may seem, it is a fundamental limitation of marine research.
The robotic gliders were key in mapping climate change and collecting data to uncover the mystery of these open ocean dead zones.
So what did they find? The data collected shows that expanding dead zones are caused by decreased oxygen in deeper waters and changes in wind patterns that bring up more nutrients from the deep ocean. This causes algal blooms to spring up and die once they deplete the nutrients available to them.
The bacteria that decompose the algal blooms deplete the water of oxygen. If this low oxygen water is not efficiently flushed away from the coast, dead zones might appear.
This analysis is pretty basic, but it has led scientists to wonder what is causing the changing wind patterns. The researchers at Oregon State suspect climate change.
However, ensuring that the cause is indeed climate change means analyzing the ocean for long periods of time. That is what gliders will do for science in the future.
The data they will provide will hopefully help diagnose the cause of these dead zones.
Grace Brush, a professor of Geography and Environmental Engineering at Hopkins has a possible answer for the cause of these massive aquatic die-offs. "It appears that the recent dead zones are in large part a result of the widespread use of synthetic nitrogen as a fertilizer for agricultural crops, particularly since the mid 20th century," Brush said.
This reasoning agrees with the suspicions of the Oregon State researchers who believe that human impact is causing these dead zones. Also, since the use of synthetic nitrogen as a fertilizer has increased from the mid-20th century to the present, it is likely that there will be an increase in the number of dead zones.
Brush's research analyzes the complex role of nitrogen in the environment. Excess nitrogen is a major cause of ecosystem deterioration in water and is particularly difficult to correct due to its vast sources and the complexity of nitrogen transformation.
After reviewing the known history of coastal deterioration worldwide, Brush proposes that a significant reduction in nitrogen is fundamental to slowing and eventually halting this deterioration.
As time passes, dead zones will become a more urgent problem. If action is not taken, the outlook may be bleak. How big will the dead zones be, how long will they last and how low will the oxygen go?
Researchers such as Grace Brush have proposed solutions to this problem; it is now up to society as a whole to act before it is too late.
