The world’s oceans have grown significantly darker over the past two decades, with 75 million square kilometers of water losing measurable light, according to a recent study in Global Change Biology. This widespread phenomenon is driven by complex environmental processes and threatens marine ecosystems by shrinking the sunlit zone where most oceanic life exists.
Researchers found that this reduction in sunlight has major implications for biodiversity, global fisheries, and even climate regulation. The darkening of the oceans affects phytoplankton, microscopic organisms that form the base of nearly every marine food web and generate about half the Earth’s oxygen. This has cascading effects on marine ecosystems, making light loss a high-priority environmental issue.
Climate change and ocean currents are believed to be contributing factors in this phenomenon. Areas with major changes in ocean circulation and warming driven by climate change are exhibiting marked declines in water clarity. Global heating may intensify water stratification, trapping organic matter and pigments near the surface, further obstructing light.
The darkening of the oceans compresses biodiversity into a thinner band as species are forced to move closer to the surface due to decreasing light levels. This compression threatens delicate balances in food webs and accelerates stress on both prey and predator populations.
The effects of darkening seas ripple beyond ocean life, with implications for climate regulation and human livelihoods. Coastal waters, being closest to human activity, are particularly vulnerable, and their resilience is crucial for both ecological health and human wellbeing. Fishing communities may also see their resources depleted as marine populations migrate or decline due to habitat compression.
While some areas have become lighter over the same period, scientists caution that this does not necessarily mean a positive reversal. Brightening may indicate reduced plankton concentrations, another red flag for marine ecosystems. Understanding the drivers behind these diverging light trends is now a priority for marine researchers and environmental policy-makers alike.
Source: https://dailygalaxy.com/2025/05/earths-oceans-are-going-dark