The National Aeronautics and Space Administration has been collecting data on phytoplankton blooms using satellite imagery.
"Inclusion of satellite data into this kind of biogeochemical modeling is really exciting," NASA scientist Jeremy Werdell said, according to United Press International.
The satellite images illustrate that the most common phytoplankton, called diatoms, have decreased approximately 1 percent per year between 1998 and 2012.
Diatoms are single-celled algae that develop as individual organisms or in colonies in the shape of small threads or ribbons. These algae have transparent cell walls and are some of the most significant organisms found in marine ecosystems. In general, phytoplankton species are the main producers for all oceanic food chains. They play an important role in exchanging carbon dioxide for oxygen via photosynthesis.
"Phytoplankton play an important role in exchanging carbon dioxide for oxygen."
NASA satellite imagery can track phytoplankton blooms by measuring the chlorophyll levels in the oceans but are still unable to distinguish between the different species. Using the satellite imagery with complex ocean models that simulate the development of different algae blooms can allow scientists to better understand the health of the bloom and the individual organisms.
Diatoms' role in removing carbon dioxide from Earth's atmosphere
In 2012, after an eight-year analysis involving scientists from around the world, researchers were able to explain how diatoms were able to remove carbon dioxide from the atmosphere by pulling excess carbon dioxide deep into the oceans. Experts from the Alfred-Wegener Institute for Polar and Marine Research in Germany found a correlation between high levels of iron and decreased levels of atmospheric carbon dioxide in ice cores, according to The New York Times.
To test this relationship, researchers found a 40-mile-wide swirling column of self-enclosed water not affected by the surrounding water currents, otherwise known as an eddy. The scientists added very high concentrations of iron (approximately 14 tons of iron (II) sulfate) into the eddy. The increase in iron induced a massive algae bloom that grew over 325 feet deep in the ocean. The photic zone (the area where light can penetrate through water) varies; however, this bloom showed that very little light is needed for algae to thrive and grow.
"We could see the bloom developing and increasing in size like a big cloud," said Dr. Victor Smetacek of the Alfred-Wegener Institute for Polar and Marine Research.
The researchers watched the diatoms as the phytoplankton formed intricate, large colonies for a total of five weeks. There were no natural predators in the eddy (such as krill), and during the five-week time frame, the organisms were able to demonstrate exponential growth, which lead to a natural form of competition. Over time, this resulted in the death of organisms that were not able to compete, causing a large portion of the diatoms to die and sink to the ocean floor. They obtained the carbon dioxide taken in from the atmosphere.
These findings have allowed scientists to better understand the carbon cycle and its potential to help prevent further increases in atmospheric carbon dioxide, causing warming waters and climate changes throughout the planet.
"Phytoplankton blooms are all over, but their fate was not previously known," said Smetacek explained to the Times. "While the experiment was going on, we saw the stocks start to sink—they went down very fast. I was very excited to see this happening."
NASA imagery providing a holistic approach to understanding the decline of algae blooms
"By combining satellite data, models and additional environmental information, you can start telling a more holistic story," NASA oceanographer Jeremy Werdell said.
This research published in the journal of Global Biogeochemical Cycles illustrated that diatoms are declining because the mixing layer of water is becoming more shallow. This means that the photic zone mixes with fewer nutrients from deeper layers in the ocean. The most significant decrease in the mixed layer occurred in the North Pacific. This location had a decline in all three of the major nutrients (iron, silicate and nitrate). In the northern middle latitudes, including the North Central Pacific and Atlantic oceans, nutrients were in limited supply, which correlated to smaller phytoplankton species. Cyanobacteria populations have declined 1.56 percent per year in the Atlantic Ocean, and coccolithophores population declined 2.06 percent per year in the North Central Atlantic Ocean over the last 15 years. With these populations decreasing, smaller phytoplankton species are not capable of carrying atmospheric carbon dioxide to the sea floor.
Researchers did not have conclusive reasons for the shallow ocean layer, but they predicted that the shifting wind patterns and the increased melting glaciers may contribute to the problem.
"Cyanobacteria populations have declined 1.56% per year in the Atlantic Ocean."
Effects of algae blooms on ocean chemistry
According to the North Carolina Department of Environmental Quality, algae blooms (a type of phytoplankton) have dramatic effects on water chemistry, specifically pH and dissolved oxygen. During the process of photosynthesis, algae remove carbon dioxide from the atmosphere and convert it into oxygen and simultaneously increase the pH (> 8.0) of the water because of the increase of hydroxide ions. During cellular respiration, the reverse reaction occurs and produces carbon dioxide, which decreases the hydroxide ions and therefore lowers the pH level. During photosynthesis, algae blooms produce high quantities of oxygen and will frequently lead to a super saturation of dissolved oxygen. Oppositely, during respiration, the algae blooms remove dissolved oxygen. The same rises and falls of pH and dissolved oxygen can occur when algae blooms die and decompose. Consumers and local fisheries should understand these values and have water quality laboratories record the changing water chemistry so local agencies can be better prepared.
It is important to understand the impacts phytoplankton have on marine ecosystems and surrounding coastlines. People rely on these ecosystems to supply them with food and recreation, as well as to support local economies. With the changing climate affecting the phytoplankton production, ecological consulting services would provide local governments with a plan to preserve and rehabilitate their current ecosystems.