By Jim Steele
All humans and animals require oxygen to live. So, to evoke public fear, headlines often claimed global warming will cause ocean life to suffocate. They evoke the true but misleading factoid that warmer water holds less oxygen. Thus, rising CO2 will cause the ocean to hold less oxygen leading to suffocation. Dishonestly, they ignore more important dynamics controlling oxygen.
As illustrated (graphic A), ocean surface temperatures reach 25°C to 30°C (red) and rapidly cool to just 5°C (blue) at 1000-meter depths. Yet in contrast to climate crisis narratives, oxygen levels (graphic B) are highest in the warm surface layers and then become severely depleted to their lowest levels at cold 1000-meter depths. Temperature is simply not the oxygen control knob.
The high concentrations of oxygen in the upper ocean layers are produced when photosynthesizing phytoplankton split water molecules. In fact, most scientists have determined that not only do phytoplankton provide oxygen for ocean life, but 50% of all the oxygen we breathe is produced by ocean phytoplankton that’s then released into the atmosphere.
The organic matter produced in the ocean’s sunlit surface layers gradually sinks. As the organic matter is consumed, oxygen is consumed, and CO2 is released. Virtually all that organic matter is consumed by the 1000-meter depths, explaining why oxygen reaches its lowest levels by 1000 meters. All that sinking matter feeds the abundant marine life in what is known as the twilight zone, the 200 to 1000-meters depths that lacks enough light for photosynthesis. Scientists now estimate that 90% of the oceans’ biomass lives and feeds in the twilight zone, fed by organic matter produced by photosynthesis in the warmest surface layer.
It has been well-proven that the increase in CO2 concentrations has increased photosynthesis, which benefits all marine life in the twilight zone. All photosynthesizing plants and algae depend on one key enzyme known as RUBISCO. RUBISCO evolved during the earth’s earliest history when the atmosphere consisted over 6000 ppm CO2 and less than 2% oxygen. Thus, RUBISCO has the ability to incorporate either oxygen, which causes detrimental photorespiration, or incorporate carbon dioxide, which makes the sugars that are the building blocks for all organic tissue. The ratio of oxygen to carbon dioxide determines photosynthesis efficiency. More oxygen or less carbon dioxide depresses photosynthesis.
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