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Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen (O 2) at increased partial pressures.Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lungs, and eyes.
Hypolimnetic oxygen depletion can lead to both summer and winter "kills". During summer stratification, inputs or organic matter and sedimentation of primary producers can increase rates of respiration in the hypolimnion. If oxygen depletion becomes extreme, aerobic organisms, like fish, may die, resulting in what is known as a "summer kill". [8]
[100] [101] According to the IPCC 2019 Special Report on the Ocean and Cryosphere in a Changing Climate, the viability of species is being disrupted throughout the ocean food web due to changes in ocean chemistry. As the ocean warms, mixing between water layers decreases, resulting in less oxygen and nutrients being available for marine life. [102]
Many gases have toxic properties, which are often assessed using the LC 50 (median lethal concentration) measure. In the United States, many of these gases have been assigned an NFPA 704 health rating of 4 (may be fatal) or 3 (may cause serious or permanent injury), and/or exposure limits (TLV, TWA/PEL, STEL, or REL) determined by the ACGIH professional association.
Oxygen is required by all aerobically respiring plants and animals and it is replenished in daylight by photosynthesizing plants and algae. Under eutrophic conditions, dissolved oxygen greatly increases during the day, but is greatly reduced after dark by the respiring algae and by microorganisms that feed on the increasing mass of dead algae.
Open ocean areas with no oxygen have grown more than 1.7 million square miles in the last 50 years, and coastal waters have seen a tenfold increase in low-oxygen areas in the same time. [23] Measurement of dissolved oxygen in coastal and open ocean waters for the past 50 years has revealed a marked decline in oxygen content.
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The pelagic food web, showing the central involvement of marine microorganisms in how the ocean imports nutrients from and then exports them back to the atmosphere and ocean floor. A marine food web is a food web of marine life. At the base of the ocean food web are single-celled algae and other plant-like organisms known as phytoplankton.