Jan. 17, 2012

Why the Sea is Blue

by Coastal Studies for Girls

Click to enlarge images

The ocean’s water looks blue to our eyes because the water absorbs the red, orange and yellow light that comes from the sun, leaving the blue light for us to see.

by Sage and Loraine, Coastal Studies for Girls

Recently, the girls here at Coastal Studies for Girls had the pleasure to hear a guest lecture by Dr. Collin Roesler. She is the chair of the Earth and Oceanographic Science Department at Bowdoin College. She joined us for dinner and delighted us with stories of phytoplankton and the Arctic and the Antarctic.

Her presentation focused on phytoplankton blooms, which occur when species of microscopic algae in the sea flourish at certain times of the year. She explained how there are some toxic phytoplankton blooms, called red tides, composed of certain species of dinoflagellates. These can be potentially hazardous to the animals in the bloom area. Phytoplankton blooms can poison shellfish, bivalves such as clams or mussels which get their food by filter feeding. When the shellfish eat the toxic phytoplankton they become contaminated with the dinoflagellates. Although red tides do not necessarily hurt the shellfish themselves, when the shellfish are caught and humans eat them, the dinoflagellate poison can make people sick. This can hurt the shellfish industries because when there are toxic phytoplankton blooms the state will shut down the area to fishing, or to digging of clams. Then clammers and other fisherman will suddenly be out of business because of a toxic algal bloom.

Some phytoplankton that we observed in our lab when we did a plankton tow off the shore near Coastal Studies for Girls.

Another problem is that blooms of dinoflagellates travel. When the wind or currents move the phytoplankton, the bloom can affect shellfish over a wide area. Thus red tides can impact our whole Maine coast. Dr. Roesler focused also on the trends of algae blooms over the years in the Gulf of Maine. She had been studying why phytoplankton blooms have been occurring more frequently in areas where they did not used to occur.

She also talked about optics and light. She explained to us how researchers are able to "see" phytoplankton from space. She can detect blooms using optics and light and the detection abilities of satellites and therefore prevent the harvesting of poisoned shellfish.

Our group asked many questions about color, and why certain phytoplankton blooms turn the colors that they do. We talked about why certain things absorb certain wavelengths and why others absorb other wavelengths. We talked about phytoplankton’s pigments and how they interact with light giving rise to different colors we see. We talked about how phytoplankton are like plants because they photosynthesize. They absorb light, which they use in photosynthesis, releasing oxygen in the process.

Collin taught us about the electromagnetic spectrum and how sunlight gives everything colors. She explained why we see flowers, trees, and snow as different colors. She also told us -- to our amazement -- why the ocean is blue. It reflects blue light and absorbs red, orange, and yellow light, thus appears blue. She explained how, if you went deep enough into the ocean, it would look black. This is because the light can’t penetrate that deep. That makes it so that water cannot absorb and reflect any light and cannot have a color.

She also explained how phytoplankton absorb and reflect certain light wavelengths. That’s why if you look from space you can see big patches of green, teal, and sometimes red. Those big patches are different phytoplankton species' blooms. During a “red tide” or plankton bloom the dinoflagellate species will absorb different colors and then they will reflect particular colors that satellites can detect from space. They will reflect colors such as red, purple, blue, or sickly green.

Overall, Dr. Roesler’s presentation was exceedingly helpful. We had just been introduced to the electromagnetic spectrum in class and it was nice to have this reinforced with a presentation on color. We all enjoyed listening to her enthusiastic lesson.

Coastal Studies for Girls is the country’s only residential science and leadership semester school for 10th grade girls. CSG is dedicated to girls who have a love for learning and discovery, an adventurous spirit, and a desire to challenge themselves.

About Coastal Studies for Girls

Coastal Studies for Girls is the country’s only residential science and leadership semester school for 10th grade girls.

The views expressed are those of the author and are not necessarily those of Science Friday.

Science Friday® is produced by the Science Friday Initiative, a 501(c)(3) nonprofit organization.

Science Friday® and SciFri® are registered service marks of Science Friday, Inc. Site design by Pentagram; engineering by Mediapolis.