Deciphering the ancient mysteries of ‘marine snow’
The planet’s largest carbon sink is deep underwater and little understood. Kaya Wilson reports.
Ocean-warming over the past century may be impacting one of the largest but least understood components in the global carbon cycle: massive deep-sea deposits of "marine snow".
The term is used to describe organic matter and detritus falling to the ocean floor. The material functions as Earth’s largest carbon sink and is the main mechanism of carbon dioxide removal from the oceans and atmosphere.
The growth of this carbon sink over millions of years may be responsible for the removal of carbon dioxide from the atmosphere about 50 million years ago, triggering the transition from a hothouse to an icehouse climate around 35 million years ago.
Research led by Adriana Dutkiewicz from the EarthByte Group at the University of Sydney, Australia, for the first time attempts to quantify the size and rate of marine snow deposits that have accumulated over the last 120 million years.
The results are published in the journal Geology.
The accumulation of marine snow leads to thick carbonate layers that settle on the ocean floor. These are subject to tectonic processes and may experience uplift to become visible geological features – such as the well-known White Cliffs of Dover. Below a certain depth however, the snow dissolves.
Dutkiewicz and colleagues modelled the formation and dissolution of the carbonate layers, as well as their movement with the Earth’s tectonic plates and subduction into the Earth’s mantle, a process known as the long-term carbon cycle. Determining the accumulation rates drew on a global network of ocean drilling cores, seabed samples and calculating variation in ocean depth through time.
They found that marine snow accumulation doubled over the past 50 million years, setting up conditions for increased glaciation from around 35 million years ago.
They suggest results that the formation of the Himalayan river systems and the weathering of the Deccan Traps during this time period may have greatly increased the supply of calcium and bicarbonate ions required by marine organisms to form the calcium carbonate of marine snow.
“Deep-sea carbonates represent a huge volume, so even small changes in the sequestration of carbonate carbon into this enormous sink are quite important for understanding net changes in atmospheric carbon dioxide and climate,” says Dutkiewicz.
The research will assist climate scientists better estimate how current climate change will affect the ability of marine snow to act as a carbon sink.
“We need to understand better how the ocean’s capacity to store CO2 will be affected by future warming,” says EarthByte team leader Dietmar Muller.
“Ocean acidity has increased by 30% since 1800, reducing the capacity of the ocean to store away carbon.”