you're reading...

Atmospheric Chemistry

Tiny plankton make big clouds brighter


McCoy, Daniel T., et al. “Natural aerosols explain seasonal and spatial patterns of Southern Ocean cloud albedo.” Science Advances 1.6 (2015): e1500157. DOI: 10.1126/sciadv.1500157


Have you ever looked up at the clouds and wondered where they come from? What causes clouds to form? Clouds affect Earth’s climate in complex ways, but our understanding of what controls clouds and their effects on climate is limited.

Satellite image showing phytoplankton blooms and clouds in the South Atlantic Ocean (NASA Earth Observatory, December 2014)


On a hot day when the sun is bright, you might have noticed that wearing lighter clothing keeps you cool. This is because dark clothing absorbs sunlight, while light clothing reflects the sun’s energy away.  When sunlight hits the earth’s surface, it is either absorbed or reflected. The same thing happens to clouds. White clouds in our atmosphere are very good at reflecting sunlight back to space. The brighter the cloud, the more energy is reflected. Clouds are not all created equal, and some types of clouds are much brighter than others. The brightness of a cloud depends on tiny particles called aerosols which act as seeds for cloud droplets to form.

There are many types of small aerosol particles, both natural and man-made, which can act as seeds for cloud growth. One important cloud-forming aerosol is the sulfate gas aerosol. These aerosols are often produced by volcanic eruptions or pollution from human sources. Sulfates can also be formed by biological sources, particularly marine phytoplankton – tiny, photosynthesizing organisms that are abundant throughout the ocean. Phytoplankton also seed cloud droplets a second way by producing organic matter which becomes airborne through sea spray.

The Southern Ocean, which encircles Antarctica, is the cloudiest region on earth and is far away from human-created pollution, making it a great region to study how natural aerosols influence cloud formation. A group of researchers from the University of Washington analyzed data from one of NASA’s satellites to study the relationship between cloud brightness and phytoplankton growth. Scientists are able to estimate the phytoplankton growth through the green color produced by a pigment called chlorophyll-a, which is also found in land plants. The researchers found that high values of chlorophyll-a coincide with high cloud brightness, indicating that they are related.

Figure 1 from McCoy et al. 2015. Correlation between cloud droplet concentration (a measure of brightness) and chlorophyll-a concentration for different time periods.

Although cloud brightness and chlorophyll-a are correlated, the satellite data is not able to demonstrate that chlorophyll-a concentration is causing brighter clouds. To investigate this hypothesis, the scientists looked at model simulations with different combinations of aerosols to test how well they could recreate the observed cloud brightness. Sulfate and organic matter were able to explain the majority of spatial patterns and seasonal variations in cloud brightness.

The scientists also looked at some regions where sulfate was more important and others where organic matter was dominant. They found sulfates were more important further North where there is more sunlight and land sources of sulfate, but organic matter dominated in regions further South where there were large phytoplankton blooms.

Figure 4 from McCoy et al. 2015. Observed and model estimates of cloud droplet concentration, sulfate concentration, and organic matter aerosols which are related to chlorophyll-a concentration.

The model estimated that phytoplankton caused an increase in the amount of sunlight reflected by clouds of up to 10 W/m2 during summer. This is comparable to the amount of extra radiation reflected by clouds formed from man-made aerosols in highly polluted regions like China. These results suggest that natural aerosols can have a big impact on how clouds reflect the sun’s energy. While these results are exciting, models have limitations. In order to find out more about the effect of phytoplankton blooms on cloud brightness, the results of this study should be verified by direct measurements of phytoplankton aerosols in the Southern Ocean. Studies like this are useful in guiding observational scientists to decide what to focus their research on and where to go to sea.
Clouds have an enormous impact on weather and climate, by regulating how much heat is trapped at Earth’s surface. This research is demonstrates how ocean plankton can alter the effect of clouds on our climate, and this understanding will improve our ability to model and predict future climate changes.


No comments yet.

Post a Comment


  • by oceanbites 2 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 3 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 4 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 5 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 7 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 8 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 8 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 9 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 9 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 10 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 11 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 11 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com