Climate Change, the Oceans, and the Oxygen Cycle

Two Thirds of Earth's Atmospheric Oxygen is Estimated to come from the Oceans

The ocean absorbs most of the heat and an estimated 30-40% of the carbon dioxide (CO2) resultant from climate change, leading to the disruption of vertical and horizontal flows of water, flows and concentrations of oxygen, carbon dioxide, salinity, and other molecules and nutrients. This happens on a global scale. Oxygen and other gases is lost more easily from warmer water into warmer air. Additionally, increased CO2 gaseous raises tilts the inorganic carbon equilibrium in seawater to increase HCO3-, H+, and Ca2+, while reducing CO32- (which is more basic than HCO3-) and CaCO31. This is the driver of ocean acidification, which is harmful to many marine organisms, particularly shell-forming species.2 The combination of and feedbacks between increased CO2, increased temperature, decreased dissolved oxygen, and decreased pH amplify stress on most marine organisms more than their simple addition could be expected to.


1. In oceanic conditions, bicarbonate makes up around 89% of dissolved inorganic carbon. Dissolved inorganic carbon includes predominantly bicarbonate, carbonate, carbon dioxide, carbonic acid, and calcium carbonate.

2. The ocean in historic time has been in an alkaline (basic) state, so the effect of acidification so far has been to decrease its basicity rather than actually going in to acid territory. From 1751-2004 the change has been estimated to be from about pH 8.25 to pH 8.14. Since pH is assigned on a base 10 logarithmic scale, this actually represents a 30% increase in H+ ions, since on a logarithmic scale with base 10, a change of 1 whole point will be 10x or 1/10th. source for pH change number and timescale
Also, the ionic environment now and in the near future is not sufficiently acidic to dissolve calcium carbonate shells; instead, it is unbalanced enough to interfere with the biological shell formation processes of many species.

Meanwhile, all this, and the related massive algae blooms play into the increase in 'dead zones' of waters depleted of oxygen. The sudden fallout of huge amounts of deceased singled-celled organisms then uses up more oxygen and releases methane, a potent greenhouse gas, and CO2 as they decay.

It is thought of much less, since the plants, algae, diatoms, seaweeds, and other photosynthesizing organisms are net oxygen producers, but photosynthesizers ALSO require environmental oxygen to breathe (operate their metabolic structures) and live, not only CO2 and sunlight and water. So dead zones also destroy oxygen producers.

While it's hard for some people to imagine any individual or local action having a meaningful influence in mitigating climate change issues, many of the oxygen depleted dead zones are driven primarily by local human-induced factors. Namely, nutrient runoff from agriculture, aquaculture, landscaping, sewage, and such like. These are things we very much CAN do something about at the individual, household, business, local, state, and national levels. As well, every gram of carbon counts, and the excess will have to be removed from the atmosphere and ocean by photosynthesis mainly, or other processes to a lesser degree

It is important to note that major photosynthetic groups (aerobic microbes such as phytoplankton, algaes, and plants) are also those responsible for by far the greatest fraction of carbon fixation on this planet. This means that they convert carbon dioxide directly into organic molecules, thus removing the CO2 from the atmosphere and/or ocean. So, a collapse in their population from climate change reduces oxygen (much faster with the far lower O2 concentrations in aqeuous environments), reducing their population further from hypoxia, and as a result the amount of CO2 removed from the atmosphere then falls driving more climate change in a vicious cycle. The recent 2018 IPCC report states that there is now at most ten years left to reduce and begin to reverse greenhouse gas accumulation before it will produce utterly catastrophic change.

The research demonstrating the essential problem:

It's important to note here that the photic zone, where light penetrates the ocean, is only 200 meters deep, and this surface layer could be warmed much faster than the entirety of the ocean. As well, a collapse of marine oxygenation will affect the ocean far more rapidly than the atmosphere, since the molecular oxygen fraction in seawater is about 3-6ppm (parts per million) while in air it is about 21% (210,000ppm). Even accounting for density, seawater is about 900 times denser than air at sea level, but not 35-70,000 times denser.

Global warming disaster could suffocate life on planet Earth, research shows - University of Leicester Press Office, UK - December 2015. This formerly linked to a press release which is no longer there. It now links to the paper listed just below.

About two-thirds of the planet’s total atmospheric oxygen is produced by ocean phytoplankton – and therefore cessation would result in the depletion of atmospheric oxygen on a global scale. This would likely result in the mass mortality of animals and humans.

The team developed a new model of oxygen production in the ocean that takes into account basic interactions in the plankton community, such as oxygen production in photosynthesis, oxygen consumption because of plankton breathing and zooplankton feeding on phytoplankton.

A link to the paper ‘Mathematical Modelling of Plankton–Oxygen Dynamics Under the Climate Change’ published in the Bulletin of Mathematical Biology is at the end of the article.