Mid-Ocean Ridge System Contributes to Global Warming; Scientists Investigate CO2 Emissions From Seafloor Spreading

Over the years, the accumulation of CO2 in the atmosphere and the ocean continues to rise steadily, raising concerns about global warming and the increased acidity of the ocean. Although CO2 emissions are attributed to human activities such as fossil fuels, it should also be noted that CO2 sources can be both manmade and natural. Throughout the history of the Earth, volcanic eruptions have strongly contributed to the carbon cycle and the evolution of the atmosphere.

Seafloor Spreading in Mid-Ocean Ridges

According to the Tectonic Plate Theory, the Earth's outermost layer is fragmented into small, large slabs of solid rock or plates constantly gliding above the mantle. The border between two plates is known as a tectonic plate boundary, which could be classified as a divergent, convergent, or transform plate boundary.

In a divergent boundary, two tectonic plates move away from each other as the molten material inside the Earth pushes its way up. In this type of boundary, the molten material cools and hardens, creating a new oceanic crust or seafloor. New crust is being made even today, but it does not affect the size of the Earth because elsewhere on the planet, the plates collide in convergent boundaries.

When one tectonic plate is pushed beneath the other, it will be subjected to high temperatures inside the Earth and will become molten material again. As the subducted material melts, it produces magma which rises to the surface of the Earth. This process results in creating a line of volcanoes in the overriding plate.

Ranges of volcanoes hidden under the sea were initially considered gentle giants of the Earth since they eject lava at a slow, steady rate along the mid-ocean ridges. However, a new study suggests that they explode on striking regular cycles, ranging from two weeks to 100,000 years. It is believed that the underwater volcanic activities that lead to seafloor spreading might also contribute to triggering natural climate swings.

CO2 Emissions from Underwater Volcanoes

Seafloor volcanoes are usually ignored because their influence is small and they are in a steady state, which they are not. Mid-ocean ridges with active volcanoes stretch across the seafloor up to around 37,000 miles. As magma is pushed out of the surface, new seafloor areas are formed, comprising up to 80% of the Earth's crust.

A 2015 study by a marine geophysicist, Maya Tolstoy of Columbia University's Lamont-Doherty Earth Observatory, found that underwater volcanoes along the mid-ocean ridge produce around eight times more lava annually than their terrestrial counterparts. Due to the chemical properties of their magmas, their CO2 emission is currently the same as from land volcanoes.

As the oceanic plates move from the mid-ocean ridge to the volcanic arc, they cross the ocean basins with sediments rich in carbonates and organic carbon. As the plates descend during subduction, these carbon sources are carried back into the mantle at 37 million tons a year. As the plate gets molten, the carbon becomes fluid and is released to the surface. This carbon, plus an additional 4 million tons released by the mantle yearly, escapes the subduction zone through volcanic eruptions.