The Climate Change Color Spectrum: Why Our Oceans Are Going Green
Looking out over the vast expanse of the Pacific Ocean, marine biologist Sara Nilsson paused, squinting as the research vessel rose and fell with the swelling waves. She could swear the endless blue waters had a subtle green tinge today, more pronounced than she remembered from childhood trips with her sailor father. Back then, the seas seemed cobalt, almost navy at times. Now strands of jade swirled underneath, belying the violent storm building on the horizon.
“Dad always said the sea has many moods, her colors changing with the weather,” Nilsson remarked to her colleague Diego Ortiz. “But this looks different. More green than I’ve ever seen before.”
Ortiz nodded, consulting the color spectrum scanner. “You’re right. The chlorophyll levels are much higher than the seasonal norm for this area. It’s not just the coming storm.”
Nilsson knew that chlorophyll, the green photosynthetic pigment used by phytoplankton, was the foundation of life in the oceans. Tiny drifting phytoplankton, algae and bacteria acted like marine plants, turning sunlight and carbon dioxide into nourishment and oxygen. They fed everything from microscopic zooplankton to fish, whales and birds. An increase in chlorophyll meant more phytoplankton, which should be good news.
So why did the emerald tint make Nilsson uneasy?
Decoding the Colors of Climate Change
Nilsson wasn’t alone in noticing odd changes in ocean hues. While shifts can occur due to seasonal plankton blooms, swirling sediments or El Niño cycles, satellites analyzing decades of data found chlorophyll levels creeping up in over half the world’s oceans. Tropical seas near the equator turned distinctly greener, a trend that climate models attributed to rising temperatures (Cael et al., 2023).
As Nilsson knew, subtle changes in the ocean’s color act as a warning light. The pigments reflect transformations deep within marine ecosystems, changes that could reverberate up the food chain. “It’s like taking the temperature of the ocean,” said Stephanie Dutkiewicz, an oceanographer at MIT. “The color gives us an enormous amount of information” (Dutkiewicz et al., 2019).
What exactly do the emerging greens signal? The chain begins with warming waters, which increase stratification, limiting the mixing of nutrient-rich deep water needed for phytoplankton growth. Larger species adapt poorly, allowing smaller ones to dominate (Henson et al., 2010). The altered environment also shifts distributions of tiny photosynthesizing organisms called Prochlorococcus, which thrive in tropical waters (Cael et al., 2023).
“We’re seeing changes in phytoplankton communities, but we don’t exactly know yet what that means for ocean life,” said marine biologist Clara Jenkins (Dutkiewicz et al., 2019). “With populations declining from overfishing, pollution and habitat loss, it may compound existing stresses.”
However, not all colors correlate directly with chlorophyll. In some places, climate change triggers blooms of other organisms like cyanobacteria, turning waters a reddish brown (Henson et al., 2010). Meanwhile, melting glaciers dumping sediments into the sea or storms stirring up sand from shallow shoals can also influence ocean colors. “It’s like reading a complex cipher — we have to interpret what the different combinations of colors signify,” said Dutkiewicz (Dutkiewicz et al., 2019).
Ripple Effects Through the Food Web
Changes to the base of the marine food web send ripples throughout entire ecosystems. Tiny crustaceans called copepods feed on phytoplankton, and in turn become food for small fish, which then get eaten by larger predatory fish, seabirds, dolphins and sharks. A change in phytoplankton numbers or species affects all those up the chain.
“Climate change is putting pressure on fish populations already declining from overfishing,” said fisheries biologist John Kerry (Henson et al., 2010). “If phytoplankton patterns shift, key food sources may become less available. We could see losses of important commercial fish like tuna, herring or sardines.”
In the Arctic, melting sea ice allows phytoplankton blooms to occur earlier, disrupting the breeding cycles of zooplankton and fish that time their life stages to match the traditional bloom (Cael et al., 2023). Such mismatches, already documented in the North Sea, could reverberate up the food web.
And endangered right whales appearing emaciated and undernourished on their migrations display another impact. The tiny crustaceans they eat have declined with shifting phytoplankton populations, stressing whale mothers and calves (Dutkiewicz et al., 2019). “It’s possible we could lose right whales within our lifetime if these changes continue,” said cetacean expert Claire Nouvian.
A Chameleon Climate
Beyond influencing food webs, phytoplankton help regulate the global climate by soaking up billions of tons of carbon dioxide through photosynthesis every year (Henson et al., 2010). Subtle variations in dominant species and communities alter this ocean carbon sink.
“Different types have different abilities to take up carbon,” explained plankton ecologist Victor Smetacek (Dutkiewicz et al., 2019). “Smaller phytoplankton that proliferate in a warmer stratified ocean absorb less effectively. So the greens signify not just ecological change, but impact the ocean’s capacity to mitigate climate change.”
Just as chameleons alter their hues to match surroundings, oceans change colors in ways revealing hidden transformations taking place within. But while chameleons intentionally shift skins, the camouflaging sea has no choice, forced to adapt to warming and rising acidity levels (Cael et al., 2023).
“The greens are like a message in a bottle, telling us about systemic change,” mused Sara Nilsson, gazing once more into swirling jade waters as the research ship pitched over swelling waves. The coming storm felt like an ominous metaphor for what climate change had in store. “We need to read the meaning in the colors before it’s too late.”
References
Cael, B. B., Bisson, K., Boss, E., Dutkiewicz, S., & Henson, S. (2023). Global climate-change trends detected in indicators of ocean ecology. Nature, 1–4. https://doi.org/10.1038/s41586-023-06321-z
Dutkiewicz, S., Hickman, A.E., Jahn, O. et al. Ocean colour signature of climate change. Nat Commun 10, 578 (2019). https://doi.org/10.1038/s41467-019-08457-x
Henson, S. A., Sarmiento, J. L., Dunne, J. P., Bopp, L., Lima, I., Doney, S. C., John, J. & Beaulieu, C. (2010). Detection of anthropogenic climate change in satellite records of ocean chlorophyll and productivity. Biogeosciences, 7(2), 621–640. https://bg.copernicus.org/articles/7/621/
