oxygen dissolution

Oxygen in oceans is disappearing, an event aided and abetted by human activity.   A paper recently published in Science studies the declining oxygen levels in global waters. As creatures that survive on oxygen, this claim is naturally alarming to us. But, it is also unclear.

Which oxygen?

Oxygen in this case does not refer to the oxygen atoms locked in the hydrogen-oxygen compound that is water (good old H2O). Oxygen in oceans refers to the oxygen that is dissolved in the water. This is the oxygen that sea creatures use to breathe. Fish live underwater and have gills, but they also need oxygen to survive, like us. Unlike us, they use gills to import the dissolved oxygen for their ‘breathing.’

Why is oxygen is disappearing?

There are a few different factors contributing to this disappearance. It is simple to link these factors to human activity.

  • One reason for this disappearance is increasing global temperatures. Warmer waters cannot hold oxygen well and prevent oxygen from mixing into deeper ocean layers (so it stays in the upper layers of the ocean). The warmer temperature will then prevent more oxygen from dissolving into the waters, suffocating the creatures living there.
  • Agricultural runoff, sewage, and fossil fuel combustion introduce higher amounts of nitrogen and phosphorus into water bodies. This robs the oceans of oxygen.

Why is this a problem?

Oxygen’s role is not limited to our breathing needs. It also has a place in global nutrient systems. Its reduction alone can have a far-reaching impact on food webs because of the many sea creatures relying on the dissolved oxygen.

Oxygen-depletion also serves as a mechanism blocking the emission of more harmful gases into our atmosphere. In oxygen-rich oceans, creatures are able to feed and regulate themselves properly. When oxygen is reduced, survival is impacted and decomposition can go haywire, allowing dangerous nitrogen compounds to pollute our atmosphere.   Nitrous oxide, a by-product of this decomposition, can remain trapped in our atmosphere for a long time, worsening global warming. The downstream effects of oxygen-depletion are funneled into a negative feedback cycle that further removes oxygen from our oceans.

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There will be more studies on this, some warning of this depletion, while others soften its blow due to its long-term deterioration. Another 2015 study theorizes that ocean depletion will happen for 500 years, and then the ocean will recover after that. This sounds hopeful, in the long term, but it leaves one to wonder what damage will be done by then. The natural resiliency of the Earth’s creatures may not be able to withstand the rapid changes caused by human activity.

People who naively disregard other activity on this planet (humans are not the only ones here or there) may miss the significance of this event. Though we do not directly use the dissolved oxygen, many creatures connected to us do. The health of our oceans gives us insight into how other systems could react to climate change. These clues will help us survive, but only if we decide to see them.

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