Oxygen is disappearing from Earth’s water; this endangers marine life and human society!

If you’ve ever wondered whether fish can suffocate in water, the answer is yes.

Our planet's waters, from the tiniest pond to the vast expanse of the ocean, are experiencing a silent crisis: a rapid and dramatic decline in oxygen levels. This "aquatic deoxygenation," as scientists call it, poses a major threat not just to marine ecosystems, but to the very fabric of human society and the stability of life on Earth.

An international study in Nature Ecology & Evolution, involving researchers from GEOMAR Helmholtz Centre for Ocean Research Kiel, urges world leaders to recognise this oxygen loss as a new planetary boundary. Planetary boundaries are critical thresholds that, if crossed, can trigger large-scale and irreversible environmental damage.

Just like we need oxygen to breathe, so do aquatic ecosystems — from microscopic plankton to bigger fish. The decline in dissolved oxygen (DO) threatens the survival of countless species at all levels of the food chain.

The study reveals a disturbing trend. Across all aquatic environments, from lakes and rivers to coastal waters and the open ocean, dissolved oxygen levels have dropped substantially in recent decades. Oceanic oxygen loss may seem small at 2% since 1960, but due to the ocean's vast volume, this translates to a significant loss. Even more alarming is the case of specific regions, like the midwaters off Central California, where oxygen levels have plummeted by 40% in just a few decades.

The research team warns that this isn't just an environmental concern; it's an economic and social one too. Billions of people rely on healthy aquatic ecosystems for food, income from fisheries and tourism, and clean drinking water.
The culprit behind this oxygen depletion is a combination of factors. Global warming, fueled by greenhouse gas emissions, raises water temperatures, decreasing the amount of oxygen water can hold. Additionally, nutrient runoff from land use changes stimulates massive algal blooms. These blooms, while initially appearing productive, consume vast amounts of oxygen as they decompose, creating oxygen-depleted dead zones.

Dr Rose, lead author of the study from Rensselaer Polytechnic Institute, emphasises the urgency of addressing this issue. Adding aquatic deoxygenation to the list of planetary boundaries will focus global efforts on monitoring, research, and policy changes to protect our vital aquatic ecosystems and, in turn, human society.

The root causes are global warming and nutrient runoff from land use, explains co-author Dr Andreas Oschlies of GEOMAR. Warmer water hinders oxygen exchange between deep and surface layers, and nutrient influx fuels algal blooms that deplete oxygen further.

These oxygen-depleted zones aren't just lifeless wastelands; they have a ripple effect that threatens our planet's health. Microbes in these zones produce potent greenhouse gases like nitrous oxide and methane, contributing further to global warming and exacerbating the very problem they were created by.

We are approaching critical thresholds, warns Professor Rose. Aquatic deoxygenation disrupts the delicate balance of Earth's climate system. Addressing the root causes, like climate change and unsustainable land practices, is crucial.