There are significant causes for concern regarding the content of oxygen in the ocean, however. So while there are many things to worry about in our climate future, the availability of oxygen for air-breathing organisms (including humans) isn't one of them. Models show that the content of oxygen in the atmosphere will experience a minute change over the next 100,000 years in response to fossil fuel use. The projected decline in atmospheric oxygen, even in the worst-case scenarios with massive fossil fuel burning and deforestation, will be very small relative to the very large atmospheric reservoir. If photosynthesis in the ocean and on land stopped producing oxygen, we could continue breathing for millennia, though we would certainly have other problems. If we were to cut or burn all forests and oxidize all organic carbon stored in vegetation and top soils worldwide, it would only lead to a small depletion in atmospheric oxygen. How about future trends of atmospheric oxygen? As early as 1970, the prominent geochemist Wally S Broecker recognized that if we were to burn all known fossil fuel reserves, we would use up less than 3% of our oxygen reservoir. Therefore, the oxygen we currently breathe comes from the slow accumulation of O 2 in the atmosphere supported by the burial of organic matter over very long time-scales-hundreds of millions of years-and not from the contemporary production by either the land or ocean biosphere. A similar process occurs on land too, with some carbon stored in soils. The tiny amount of oxygen which had been generated to produce this carbon store can later be released to the atmosphere. This organic carbon may eventually turn into fossil fuels such as coal, oil and gas. In fact, the net production of oxygen in the ocean is close to 0.Ī tiny fraction of the primary production, roughly 0.1%, escapes degradation and is stored as organic carbon in marine sediments-a process referred to as the biological carbon pump. Most of the oxygen produced by the ocean is directly consumed by the microbes and animals that live there, or as plant and animal products fall to the seafloor. But it's not responsible for 50% of the air we humans breathe. So yes, the ocean is responsible for about 50% of the oxygen produced on the planet. Today, roughly half of photosynthesis takes place in the ocean and half on land. Oxygen has been relatively stable at a high level for the past 500 million years. This oxygen is derived from photosynthesis-the process by which plants turn carbon dioxide and water into organic matter and oxygen. It is the advent of microscopic ocean bacteria and plants (phytoplankton) and, later, larger plants on land which caused the staggering increase of oxygen in our atmosphere. The atmosphere is now made up of 21% oxygen, but it accounted for just 0.001% of today's levels during the first 2 billion years of Earth's history. The Earth's atmosphere has not always been as rich in oxygen as it is today. While they may be good fodder for speeches, these claims misrepresent where the oxygen we breathe actually comes from, and in doing so, mislead the public as to why we should step up our role as ocean custodians.
These mantras are repeated by high-profile politicians, including US climate envoy John Kerry and French president Emmanuel Macron, international organizations such as Unesco and the European Commission, and even prominent reports from the IPCC and other reputable scientific institutions. To shed light on this, statements such as "the ocean provides 50% of the oxygen we breathe," or its equivalent, "every second breath we breathe comes from the ocean," have become common mantras to highlight human dependence on the ocean and the risk of lower oxygen supply due to climate change and environmental degradation.
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