Earth’s 10th Tipping Point Identified: What It Means for Our Planet

A staggering 700 sites worldwide were affected by low oxygen conditions in 2011, up from just 45 before the 1960s. Globally, oceans have lost around 2% of dissolved oxygen since the 1950s and are expected to lose more in the years to come.¹

As oceans lose oxygen, marine life suffocates, with devastating consequences rippling through entire ecosystems. Scientists have identified ocean deoxygenation as a potential 10th “planetary boundary” that humanity has already crossed. 

The implications are dire, not just for marine life but for the billions of people who depend on the ocean for food and livelihoods.

Aquatic Deoxygenation

Aquatic deoxygenation is a global phenomenon where the dissolved oxygen levels in water bodies like lakes, reservoirs, and oceans are rapidly declining. Since the 1950s, the world’s oceans have lost around 2% of their oxygen, with projections suggesting a further 3-4% loss by 2100. This may not sound like much, but even slight reductions can have devastating consequences for marine life.

The primary culprits behind this silent killer are rising water temperatures due to climate change and excessive algal growth fueled by nutrient pollution from human activities. Warmer water holds less oxygen and hinders mixing between oxygen-rich surface waters and deeper, oxygen-poor layers. Meanwhile, algal blooms consume oxygen as they decompose, creating vast “dead zones” where little can survive.

Deoxygenation is closely linked to other planetary boundaries like climate change and biogeochemical flows.

As oceans lose oxygen, they release potent greenhouse gases like nitrous oxide and methane, further exacerbating global warming in a vicious feedback loop. Nutrient pollution from agriculture and sewage also fuels algal blooms that deplete oxygen.

A Ripple Effect on Marine Ecosystems

The impacts of deoxygenation are far-reaching and complex. Fish, which are highly susceptible to oxygen depletion, face reduced growth, reproduction, and survival rates.^(ref)

As populations dwindle, entire food webs are disrupted, potentially leading to the collapse of entire ecosystems. Even slight changes in oxygen levels can induce stress in marine organisms, depriving them of adequate oxygen at the tissue level.

Deoxygenation also alters species distributions and interactions. Mobile species like fish may shift to shallower, more oxygenated waters, increasing competition and vulnerability to fishing. Sessile organisms like corals and sponges face localized extinctions. These changes reverberate through food webs, potentially reducing biodiversity and productivity.

The Human Cost of a Suffocating Ocean

As the oceans gasp for breath, the consequences for humanity are equally dire. Deoxygenation not only threatens the intricate web of marine life but also the livelihoods and food security of millions who depend on fisheries. Declining fish stocks could lead to economic losses and social upheaval in coastal communities worldwide.

Over 3 billion people rely on wild-caught and farmed seafood as a primary protein source.^(ref) Deoxygenation jeopardizes this critical food supply by reducing fish growth, reproduction, and survival. In the Baltic Sea, recurring hypoxia has contributed to smaller sizes and lower abundance of Atlantic cod, an economically important species.

Moreover, the ocean’s capacity to absorb carbon dioxide and regulate Earth’s climate is compromised by deoxygenation. This undermines the ocean’s role as a vital carbon sink that has absorbed about 30% of anthropogenic CO₂ emissions.

A Call to Action

The identification of aquatic deoxygenation as a potential planetary boundary is a wake-up call for humanity. We must act swiftly and decisively to address the root causes of this crisis, including curbing greenhouse gas emissions and reducing nutrient pollution from agriculture and sewage.

Mitigating deoxygenation requires a multi-pronged approach:

• Dramatically reducing greenhouse gas emissions to limit global warming to well below 2°C, in line with the Paris Agreement
• Improving wastewater treatment to remove nitrogen and phosphorus before discharge
• Implementing sustainable agricultural practices to minimize fertilizer runoff
• Protecting and restoring coastal ecosystems like mangroves and seagrasses that absorb nutrients and store carbon
• Strengthening governance at local to global scales to manage nutrient inputs and fisheries
• Enhancing monitoring networks to track deoxygenation trends and impacts
• Supporting research to better understand the drivers, thresholds, and consequences of oxygen loss

Failure to do so could push our planet’s life-sustaining waters past the point of no return, with catastrophic consequences for marine life and human society.

Source:

1. International Union for Conservation of Nature