Recent satellite data reveals a concerning trend: over the past two decades, 21% of the Earth’s oceans have darkened, raising significant alarms for marine ecosystems and the life that relies on them. This study, published in the Global Change Biology journal, warns that the darkening of ocean waters could have severe consequences for marine biomes and fisheries, which are vital to both the ocean’s health and human economies.
Professor Thomas Davies from the University of Plymouth conducted this research and highlighted the critical role of the photic zones, where sunlight penetrates to support marine life. These zones, ranging from the surface to approximately 200 meters, are essential for sustaining marine food webs and fisheries. The study utilized NASA’s Ocean Color Web data to analyze changes in light penetration over time, revealing a 21% increase in ocean darkening between 2003 and 2022. This data suggests that the photic zones are becoming progressively shallower, with 9% of the oceans exhibiting a decrease of 50 meters in depth, and 3% experiencing a 100-meter decline.
The darkening of the oceans is attributed to global warming and shifts in ocean currents, which can alter the distribution of light and nutrients in marine environments. Despite this overall trend of darkening, certain regions of the ocean have shown an increase in light, particularly in coastal areas, but this does not compensate for the overall reduction in photic zone depth.
Professor Davies predicts that the implications of this darkening could be severe, potentially disrupting marine food webs, affecting global fisheries, and altering the planet’s carbon and nutrient cycles. The study also emphasizes the need for continued monitoring and research to understand how these changes will impact marine biodiversity and the economies that depend on it.