Oceans worldwide have darkened significantly over the past two decades, raising concerns about the impact on marine life and ecosystems, according to a recent study.
Oceans around the globe have become darker over the last two decades, prompting serious concerns among researchers regarding the health of marine ecosystems. A study led by Professor Thomas Davies from the University of Plymouth, published in the journal Global Change Biology, highlights the alarming trend observed in satellite data.
According to data from NASA’s Ocean Color Web, 21% of the planet’s oceans have darkened between 2003 and 2022. This darkening trend poses a significant threat to marine life, particularly in the photic zones of the ocean, where light penetration is crucial for various biological processes.
The photic zone extends to about 200 meters deep and is vital for sustaining global fish populations and nutrient cycles. It is within this zone that marine organisms depend on both sunlight and moonlight for essential activities such as hunting, mating, and reproduction.
As the oceans darken, creatures that rely on light may be forced to move closer to the surface, potentially leading to overcrowding in these critical habitats. The upper layers of the ocean are home to microscopic organisms and various types of plankton, which are foundational to the marine food web.
Using satellite data and an algorithm to measure light attenuation in seawater, Davies was able to assess the depth of photic zones worldwide. The findings revealed that in areas where the oceans have darkened, 9% of photic zones have become shallower by 50 meters, and 3% have decreased by 100 meters.
The reasons behind the darkening of oceans, particularly in offshore areas, remain unclear. However, the study suggests that global warming and changes in ocean currents may play a role in this phenomenon.
Interestingly, while the overall trend indicates a darkening of the oceans, about 10% of the ocean surface, equivalent to 37 million square kilometers, has experienced an increase in light over the past two decades. Coastal areas, in particular, have seen a rise in light levels. Nevertheless, this increase does not result in a net reduction in photic zone depth near shorelines.
Davies warns that the implications of ocean darkening could be severe, affecting marine food webs, global fisheries, and the overall carbon and nutrient budgets of the oceans. The study underscores the urgent need for further research to understand the long-term effects of these changes on marine life and ecosystems.
As scientists continue to monitor these trends, the findings serve as a critical reminder of the interconnectedness of ocean health and the broader environmental challenges facing our planet.
Source: Original article