The disappearance of sea ice in polar regions due to global warming not only increases the amount of light entering the ocean, but also changes its color.
The disappearance of sea ice in polar regions due to global warming not only increases the amount of light entering the ocean, but also changes its color. These changes have far-reaching consequences for photosynthetic organisms such as ice algae and phytoplankton. That is the conclusion of new research published in Nature Communications, led by marine biologists Monika Soja-Woźniak and Jef Huisman from the Institute for Biodiversity and Ecosystem Dynamics (IBED) at the UvA.
The international research team, which also included physical chemist Sander Woutersen (HIMS) and collaborators from the Netherlands and Denmark, investigated how the loss of sea ice alters the underwater light environment. Sea ice and seawater differ fundamentally in how they transmit light. Sea ice strongly scatters light and reflects much of it, while allowing only a small amount to penetrate. Yet, this limited amount of light still contains almost the full range of visible wavelengths. In contrast, seawater absorbs red and green light, while blue light penetrates deep into the water column. This is what gives the ocean its blue color.
Molecular Vibrations of Water
Another key difference between ice and liquid water lies in the role of molecular vibrations. In liquid water, H₂O molecules are free to move and vibrate, which leads to the formation of distinct absorption bands at specific wavelengths. These bands selectively remove portions of the light spectrum, creating gaps in the light available for photosynthesis.
Read more at Universiteit van Amsterdam
Image: The bottom of a cut-out block of 2 m thick ice covered with ice algae, placed atop the sea ice of McMurdo Sound, Antarctica. (Credit: Photo by Lars Chresten Lund-Hansen)
