This article helps explain why species of phytoplankton are exploding in recent years ….. to balance and increase oxygen levels. Phytoplankton die offs happen from lack of oxygen from poor conditions during the day like cloudy conditions, calm weather, warm water. When die offs occur, bacteria use more oxygen to consume dead phytoplankton and result in “dead zones” where very few animals can live. When oxygen levels are dropping faster than carbon dioxide levels that affects all oxygen-breathing organisms including humans. Click here to read the full article or an excerpt below.
New research shows oxygen depletion in the atmosphere accelerating since 2003, coinciding with the biofuels boom; climate policies that focus exclusively on carbon sequestration could be disastrous for all oxygen-breathing organisms including humans Dr. Mae-Wan Ho
Threat of oxygen depletion
Mention climate change and everyone thinks of CO2 increasing in the atmosphere, the greenhouse effect heating the earth, glaciers melting, rising sea levels, floods, hurricanes, droughts, and a host of other environmental catastrophes. Climate mitigating policies are almost all aimed at reducing CO2, by whatever means.
Within the past several years, however, scientists have found that oxygen (O2) in the atmosphere has been dropping, and at higher rates than just the amount that goes into the increase of CO2 from burning fossil fuels, some 2 to 4-times as much, and accelerating since 2002-2003 [1-3]. Simultaneously, oxygen levels in the world’s oceans have also been falling  (see Warming Oceans Starved of Oxygen, SiS 44).
It is becoming clear that getting rid of CO2 is not enough; oxygen has its own dynamic and the rapid decline in atmospheric O2 must also be addressed. Although there is much more O2 than CO2 in the atmosphere – 20.95 percent or 209 460 ppm of O2 compared with around 380 ppm of CO2 – humans, all mammals, birds, frogs, butterfly, bees, and other air-breathing life-forms depend on this high level of oxygen for their well being  Living with Oxygen (SiS 43). In humans, failure of oxygen energy metabolism is the single most important risk factor for chronic diseases including cancer and death. ‘Oxygen deficiency’ is currently set at 19.5 percent in enclosed spaces for health and safety , below that, fainting and death may result.
The simultaneous decrease in ocean oxygen not only threatens the survival of aerobic marine organisms, but is symptomatic of the slow-down in the ocean’s thermohaline ‘conveyor belt’ circulation system that transports heat from the tropics to the poles, overturns surface layers of into the deep and vice versa, redistributing nutrients and gases for the ocean biosphere, and regulating rainfall and temperatures on the landmasses. This dynamical system is highly nonlinear, and small changes could make it fail altogether, with disastrous runaway effects on the climate  (Global Warming & then the Big Freeze, SiS20). More importantly, it could wipe out the ocean’s phytoplankton that’s ultimately responsible for splitting water to regenerate oxygen for the entire biosphere, on land and in the sea