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Source: India Today

Context

A new study appears to show that more than one-fifth of the world's ocean has darkened significantly over the last two decades.

What is the Ocean Darkening?

• The darkening of the ocean is essentially the shrinkage of the photic zones, or the layers of water through which sunlight can enter and induce the photosynthesis process, which is necessary for all living processes.
• The photic layers can reach depths of roughly 200 meters and support nearly 90% of the world's marine life.
• This layer is responsible for improving ocean productivity, as well as regulating climate and supporting global fisheries and associated activities.
• A new study appears to show that more than one-fifth of the world's ocean has darkened significantly over the last two decades.

Why is the ocean darkening?

• Darkening in coastal zones is typically caused by increased runoff of agricultural nutrients, organic matter, and sediments into the ocean with rain, which directly supports light-blocking algae blooms.
• In the open ocean, the most likely causes include changes in plankton dynamics, rising sea surface temperatures, and changes in ocean circulation.

Research findings

The study used satellite data and advanced modeling tools. Light absorption variations were assessed using the diffuse attenuation coefficient (Kd 490). Between 2003 and 2022, 21% of the world's oceans became darker. Particularly, 9% experienced a drop in photic zone depths greater than 50 meters.

Impact on Marine Life

The shrinkage of photic zones endangers marine ecosystems. Species that rely on sunlight for feeding and reproduction may encounter competition in shallower seas. This could disturb existing food webs and cause ecological changes.

Source: Indian Express