Which phenomenon is characterized by a significant increase in sea temperature leading to coral bleaching?

The phenomenon characterized by a significant increase in sea temperature leading to coral bleaching is indeed global warming. Coral bleaching occurs when corals experience stress due to elevated sea temperatures, often linked to longer-term climate changes associated with global warming. As ocean temperatures rise, typically due to increased greenhouse gas emissions trapping heat in the atmosphere, corals expel the symbiotic algae (zooxanthellae) that live in their tissues. These algae provide corals with food through photosynthesis and contribute to their vibrant colors. Without them, corals lose their color and can become more susceptible to disease and mortality, representing a critical ecological concern for marine ecosystems.

While El Niño can also cause temporary increases in sea temperatures and has been known to trigger coral bleaching events, global warming refers to a more sustained rise in ocean temperatures over the long term, thereby having a more pervasive impact on coral reefs. La Niña typically involves cooler water temperatures, which are generally less associated with coral bleaching. Ocean stratification, referring to the layering of water masses with different temperatures and salinities, doesn’t directly cause coral bleaching, although it can influence the local marine environment.