Melting sea ice adjustments not solely how a lot gentle enters the ocean, but additionally its coloration, disrupting marine photosynthesis and altering Arctic ecosystems in refined however profound methods.
As international warming causes sea ice within the polar areas to soften, it’s not simply the quantity of daylight getting into the ocean that adjustments. The colour of the underwater gentle shifts, too, and this has main penalties for all times under the floor.
In line with new analysis printed in Nature Communications, these adjustments might considerably influence tiny however very important organisms like ice algae and phytoplankton. The research was led by marine biologists Monika Soja-Woźniak and Jef Huisman from the College of Amsterdam’s Institute for Biodiversity and Ecosystem Dynamics.
The worldwide group of scientists, which included bodily chemist Sander Woutersen and collaborators from the Netherlands and Denmark, explored how melting sea ice transforms the underwater gentle setting. Mild behaves very in another way in sea ice in comparison with open water.
Sea ice displays and scatters most daylight, letting solely a small quantity by, however that small quantity contains almost all seen wavelengths. Open seawater, then again, absorbs reds and greens, whereas permitting blue gentle to journey deeper. For this reason the ocean seems blue to our eyes.
Molecular vibrations of water
One other key distinction between ice and liquid water lies within the position of molecular vibrations. In liquid water, H₂O molecules are free to maneuver and vibrate, which ends up in the formation of distinct absorption bands at particular wavelengths. These bands selectively take away parts of the sunshine spectrum, creating gaps within the gentle accessible for photosynthesis.
Earlier analysis by Maayke Stomp and Prof. Huisman demonstrated that these molecular absorption options create ‘spectral niches’—distinct units of wavelengths accessible for photosynthetic organisms. Phytoplankton and cyanobacteria have advanced a range of pigments tuned to the completely different spectral niches, shaping their international distribution throughout oceans, coastal waters, and lakes.
In ice, nevertheless, water molecules are locked right into a inflexible crystal lattice. This fastened construction suppresses their means for molecular vibrations and thereby alters their absorption options. As a consequence, ice lacks the absorption bands of liquid water, and therefore a broader spectrum of sunshine is preserved beneath sea ice. This elementary distinction performs a key position within the spectral shift that happens as sea ice melts.
Ecological implications
As sea ice disappears and provides approach to open water, the underwater gentle setting shifts from a broad spectrum of colours to a narrower, blue-dominated spectrum. This spectral change is essential for photosynthesis.
“The photosynthetic pigments of algae residing beneath sea ice are tailored to make optimum use of the big selection of colours current within the little quantity of sunshine passing by ice and snow,” says lead creator Monika Soja-Woźniak. “When the ice melts, these organisms instantly discover themselves in a blue-dominated setting, which supplies a lesser match for his or her pigments.”
Utilizing optical fashions and spectral measurements, the researchers confirmed that this shift in gentle coloration not solely alters photosynthetic efficiency, however may additionally result in adjustments in species composition. Algal species specialised in blue gentle might achieve a powerful aggressive benefit compared to ice algae.
In line with Prof. Huisman, these adjustments can have cascading ecological results. “Photosynthetic algae type the muse of the Arctic meals net. Modifications of their productiveness or species composition can ripple upward to have an effect on fish, seabirds, and marine mammals. Furthermore, photosynthesis performs an vital position in pure CO2 uptake by the ocean.”
The research highlights that local weather change within the polar areas does greater than soften ice—it causes elementary shifts in key processes akin to gentle transmission and vitality movement in marine ecosystems.
The outcomes underscore the significance of incorporating gentle spectra and photosynthesis extra explicitly in local weather fashions and ocean forecasts, particularly in polar areas the place environmental change is accelerating at an unprecedented fee.
Reference: “Lack of sea ice alters gentle spectra for aquatic photosynthesis” by Monika Soja-Woźniak, Tadzio Holtrop, Sander Woutersen, Hendrik Jan van der Woerd, Lars Chresten Lund-Hansen and Jef Huisman, 30 April 2025, Nature Communications.
DOI: 10.1038/s41467-025-59386-x
