Written by When we think of the oxygen we breathe, towering forests and lush greenery often come to mind. But beneath the waves lies a hidden powerhouse—our oceans, responsible for producing more than half of the Earth’s oxygen. Through the quiet labor of phytoplankton, seaweed, and marine algae, the ocean sustains life far beyond its shores. It’s time we recognize and protect this vital, yet often overlooked, contributor to our planet’s breath. It may come as a surprise, but between 50% and 80% of Earth’s oxygen originates from the ocean. This incredible output is primarily thanks to microscopic marine organisms such as phytoplankton, algae, and certain bacteria, which reside in the sunlit upper layers of the sea. Through photosynthesis, these organisms convert carbon dioxide and water into organic matter, releasing oxygen as a byproduct — essentially acting as the lungs of the planet.
The Mystery of ‘Dark Oxygen’
In a groundbreaking twist to our understanding of oxygen production, scientists have discovered that oxygen can also be generated in the dark depths of the ocean, far from sunlight. Certain metal-rich minerals on the seafloor can induce a process akin to electrolysis, splitting water molecules into hydrogen and oxygen — without any photosynthetic activity. Dubbed “dark oxygen,” this phenomenon challenges the long-held belief that oxygen generation is exclusively tied to sunlight-driven processes.
A Worrying Trend: Declining Ocean Oxygen
Over the past 50 years, global oceanic oxygen levels have dropped by more than 2%. This decline is largely driven by climate change, which warms seawater and reduces its capacity to hold dissolved oxygen. Additionally, agricultural runoff and urban waste lead to eutrophication, where nutrient overloads fuel algal blooms that deplete oxygen as they decay. These conditions can create hypoxic “dead zones” — uninhabitable regions for most marine life — severely impacting biodiversity and fisheries.
Life Hanging On: Ancient Microbes in Deep-Ocean Sediments
One of the ocean’s most awe-inspiring stories comes from the South Pacific Gyre, where scientists have uncovered microbial communities buried in oxygenated sediments that are over 100 million years old. Despite extreme nutrient scarcity, these microbes persist in a near-dormant state, drawing on minuscule energy reserves. Their survival underscores the remarkable adaptability and endurance of life, even in Earth’s most remote and hostile environments.