Extensive sea ice covered the world's oceans during the last ice age, which prevented oxygen from penetrating into the deep ocean waters, a new study has found.
The findings challenge previous assumptions about the relationship between oxygen and carbon dioxide in deep ocean waters.
Understanding this relationship gives researchers important insights into how the world's oceans may respond to climate change.
The ocean plays an important role in the carbon cycle. When carbon dioxide from the atmosphere dissolves in surface waters, algae turn the carbon into organic matter.
Respiration of that organic matter removes oxygen as carbon sinks to the deep ocean. The process of transferring carbon from the surface of the ocean to the deep is known as the biological pump.
Currently, the ocean is losing oxygen and that trend is expected to continue because the solubility of oxygen decreases as temperatures warm.
Sediment collected previously from below the sea floor shows lower oxygen levels in the deep ocean during that period.
Researchers found that disequilibrium played an important role in the carbon cycle. Deep ocean oxygen concentrations were reduced because surface waters were less equilibrated with the atmosphere.
The disequilibrium was a result of the vast sea ice mainly over the Southern Ocean, as well as higher iron fertilization from the ice age atmosphere, which was dustier.
The researcher method to understand the role of sea ice and other processes in the ocean carbon and oxygen cycles could also be applied to future climate modelling.
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth.
It describes the movement of carbon as it is recycled and reused throughout the biosphere, as well as long-term processes of carbon sequestration to and release from carbon sinks.