Oxygen minimum zone

An oxygen minimum zone is a mid-depth ocean layer with much less dissolved oxygen than surface waters and the deep ocean. It forms where oxygen consumption outpaces its resupply.

Ocean deoxygenation: The decline of dissolved oxygen in ocean waters over time. Oxygen minimum zones are natural low-oxygen features that can intensify as the ocean loses oxygen.
Marine ecology: The study of interactions among marine organisms and their environments. Oxygen levels in these layers reshape species distributions and ecological interactions.
Marine nitrogen cycle: The transformations and movement of nitrogen through seawater, organisms, and sediments. Low oxygen favors nitrogen-loss pathways that can remove biologically available nitrogen from the ocean.
Eastern Tropical North Pacific oxygen minimum zone: A broad, intense oxygen minimum zone beneath the eastern tropical North Pacific. It is one of the ocean’s largest and most oxygen-poor examples.
Ocean stratification: The layering of seawater by density, which limits vertical mixing. Stronger layering can restrict oxygen transport from surface waters into mid-depth layers.
Oxygen-tolerant fish: Fish species adapted to survive at unusually low dissolved-oxygen concentrations. Such species can exploit habitats that exclude less tolerant competitors and predators.
Denitrification: Microbial reduction of nitrate or nitrite to gaseous nitrogen compounds under oxygen-poor conditions. It becomes an important route for nitrogen loss within many oxygen minimum zones.
Eastern Tropical South Pacific oxygen minimum zone: A major oxygen minimum zone beneath the eastern tropical South Pacific, off western South America. Its strong oxygen depletion is linked to productive waters and weak ventilation.
Marine snow: Sinking particles of organic matter, including dead organisms and waste, in the ocean. Its decomposition consumes oxygen as organic material sinks through the zone.
Vertical migration: The movement of marine organisms between different depths, often on a daily cycle. The zone can block or redirect migrations between surface feeding grounds and deeper waters.

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