Lasers have been used to all sorts of ends recently, from the discovery of laser smoke rings to searching for life on Mars. Now, scientists are putting lasers to work on the relationship between the climate and the ecosystem at the poles.
With the polar icecaps receding each year, it is becoming a serious matter for scientists to understand the factors involved. While we understand that climate change is one of the main factors in the ice coverage at the poles, understanding the interaction between the climate and the ocean ecosystems is also of vital importance.
Phytoplankton are essentially minute plants that live at the top of the ocean absorbing carbon dioxide and releasing oxygen.
But to conduct such large scale observation of such tiny organisms, they needed a radical solution.
The CALIPSO satellite mission is a collaboration between NASA and France’s space agency, the Centre National d’Etudes Spatiales. The University of Maine in Orono, the University of California, Santa Barbara, and Princeton University also participated in the study.
The aim was to shine a laser on the ocean surface and monitor the phytoplankton populations boom and bust cycles.
CALIOP and Phytoplankton
Phytoplankton plays a key role in the planet’s carbon cycle. It is a huge factor in carbon dioxide absorption in the upper ocean and produces oxygen, vital for life on Earth.
In the past, scientists theorised that the boom and bust nature of phytoplankton levels was linked to the predators in their environment. So if there is a boom in the fish population, there will be a corresponding bust in the phytoplankton population.
The experiments NASA and Oregon State University in Corvallis have been carrying out were designed to test this theory.
“It’s really important for us to understand what controls these boom-and-bust cycles, and how they might change in the future so we can better evaluate the implications on all other parts of the food web,” Michael Behrenfeld, a marine plankton expert from the university, said in a NASA press release on the subject.
In order to test the theory, NASA developed CALIOP, a Cloud-Aerosol Lidar with Orthogonal Polarization, and instrument aboard CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation), a satellite launched in 2006. With these instruments, scientists monitored plankton in the polar regions continuously between 2006 and 2015.
“CALIOP was a game-changer in our thinking about ocean remote sensing from space,” said Chris Hostetler, a research scientist at Langley. “We were able to study the workings of the high-latitude ocean ecosystem during times of year when we were previously completely blind.”
How did the Observation Work?
Normally, to study and measure plankton levels, organisations would measure the light reflecting of the ocean plants with various satellite sensors. However, in polar regions, there are dark skies and almost constant cloud cover limit the amount of light that satellites can pick up.
Obviously, this is a bit of a problem for constant observation!
CALIOP uses lidar instead which shines a laser and is able to illuminate and measure the plankton night or day and even through some cloud coverage.
While CALIOP Lidar was not optimised for ocean measurements, but atmospheric measurements instead, the results of this study showed that the ocean measurements are scientifically valuable.
With this satellite, the team had a significantly better opportunity to look at the changes in the phytoplankton population. And as a bonus, they showed a broader application of their engineered CALIOP Lidar.
So What Did They Find?
The scientists found that the boom and bust cycles were tied to ice cap coverage and not to do with year-to-year growth rates. This is significant because it shows that the predators aren’t exclusively linked to phytoplankton levels, ‘changes in ice cover were more important to phytoplankton population fluctuations than were differences in growth rates and predation’ (NASA).
As long as the plankton’s growth rate is accelerating, the whole ecosystem will be in a boom. However, when the plankton’s growth stagnates, other animals in the ecosystem quickly catch up, the plankton are eaten and the bloom ends. This leads to a bust cycle that inevitably leads to animals further up the food chain dying off.
With this knowledge, it is clear that the amount of ice cap coverage is directly linked with the ecosystem at large: the more ice, the more phytoplankton; the less ice, the less phytoplankton.
This study has illuminated (haha) the way that phytoplankton is linked with ice cap coverage but there are still questions to be answered about the causes of phytoplankton blooms. This knowledge is vital to gain a better understanding of the cycle of oceanic carbon and managing the health of global ocean ecosystems.
As the CALIOP Lidar was not engineered specifically for ocean measurements, NASA is now testing new lidar technology to allow scientists to better measure phytoplankton distribution in the sunlit layer of the ocean.
“The take home message is that if we want to understand the biological food web and production of the polar systems as a whole, we have to focus both on changes in ice cover and changes in the ecosystems that regulate this delicate balance between predators and prey,” said Behrenfeld (NASA).
The more understanding we have of our planet, the more we can work to tackle climate change and so the development of further laser lidar technology is of great interest to everyone. There are already plenty of great uses for lasers and we can’t wait to see what they come up with next!