The sea has better carbon storage than trees.In a warmer future, marine carbon sinks may help stabilize our planet

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The continent of Zealandia is about twice as large as India, but most of it is more than 1000 meters deep in the southwestern Pacific Ocean. Credit: Provided by the author, CC BY-ND

We consider trees and soil as carbon sinks, but the world’s oceans hold much more carbon stores and are more effective at storing carbon permanently.

New research We will investigate the long-term rate of permanent carbon removal by plankton shells in the waters near New Zealand announced today.

Indicates that the shell emits about the same amount of carbon as the area’s emissions. carbon dioxideAnd this process was even higher during the ancient period of climate warming.

Humans extract carbon from the ground by burning fossil fuels that were deposited millions of years ago and releasing them into the atmosphere as carbon dioxide. The formation rate of new fossil fuels today is very low. Instead, the main geological (long-term) mechanism of carbon storage today is the formation of shells, which are preserved as sediments. Seabed..

The continent of Zealandia sinks primarily below the Southwest Pacific, but includes the islands of New Zealand and New Caledonia.

Carbon dioxide emissions According to the burning of fossil fuels on the continent, it is about 45 million tons per year, which is equivalent to 0.12% of the world total.

Our work is documenting projects that were part of the International Ocean Discovery Program (IODP). Expedition 371 We drilled into the seabed of Zealandia to investigate how the continent was formed and analyzed the ancient environmental changes recorded in its sediments.

海は木よりも炭素の貯蔵に優れています。 より暖かい未来では、海洋の炭素吸収源は私たちの惑星を安定させるのに役立つ可能性があります

Researchers Xiaoli Zhou (USA) and Yu-Hyeon Park (Korea) will take water samples from sediment cores during the IODP expedition 371. Credits: Laia Alegret, IODP, CC BY-ND

Pull carbon into the seabed

Organic carbon in the form of dead plants, algae and animals is mostly eaten by other organisms, mainly bacteria, in both sea and forest soils.Most organisms in the ocean are so small (less than 1 mm in size) that they remain invisible, but when they die and sink, they release carbon. Deep sea.. These shells can accumulate on the ocean floor and form vast deposits of chalk and limestone.

The sediments we cored are hundreds of meters thick, Mild climate It may resemble the coming decades and centuries. You can know the past environment from fossil analysis.

Seashell made of Calcium carbonateQuarantine a significant amount of carbon. The average shell accumulation rate over the last million years has been about 20 tonnes per square kilometer per year.

With a total area of ​​about 6 million square kilometers, the average storage of calcium carbonate is about 120 million tonnes per year, which is equivalent to 53 million tonnes of carbon dioxide per year.

This is about the same as the emissions from combustion. Fossil fuel On today’s continent, it is within the margin of error of the calculation. However, fine shells are accumulating not only in Zealandia but also in a much larger area.

海は木よりも炭素の貯蔵に優れています。 より暖かい未来では、海洋の炭素吸収源は私たちの惑星を安定させるのに役立つ可能性があります

This map shows the global current and seafloor (shaded) areas where calcium carbonate shells are accumulating. credit: Rupert Sutherland, CC BY-ND

Planetary carbon cycle

Because rocks are cooked deep, the Earth naturally emits carbon dioxide from mineral springs and volcanoes. It is unlikely to be affected by climate change. The Earth stores carbon dioxide as rocks change on the surface and shells accumulate on the ocean floor. Both of these mechanisms can be affected by climate change.

The biosphere and ocean also hold significant carbon stores that are steadily changing. It’s a complex system, and many scientists are trying to understand how it reacts to human activity.

Different parts of the carbon system respond in different ways and at different speeds. Our work provides clues about what happens at sea.

About 4-8 million years ago, the climate was warm, carbon dioxide levels were equal to or higher than they are today, and the oceans were more acidic. However, the average rate of shell accumulation in Zealandia was found to be more than double that of the last million years.

This is a pattern found elsewhere in the world. In the warmer climate of this period, there were seas that produced more shells, but these data are average accumulation rates on a one million year time scale.

海は木よりも炭素の貯蔵に優れています。 より暖かい未来では、海洋の炭素吸収源は私たちの惑星を安定させるのに役立つ可能性があります

This cartoon shows how carbon moves through the Earth’s system. Credits: Rupert Sutherland, CC BY-ND

The mechanism by which these ancient warmer seas produced more shells is the subject of ongoing research (including us).

Rivers and winds nourish the ocean, especially during extreme weather, and changes can occur on a short time scale.In the other extreme case, it is fully integrated Climate model It shows that large-scale reorganization of ocean currents to enhance the supply of nutrients from the deep sea can take centuries or even thousands of years.

Our work emphasizes and quantifies the important role that the ocean, especially the microscopic life within it, ultimately plays in restoring the balance of our planet. The rate at which dead plankton draws carbon into the deep sea and small shells store it permanently on the ocean floor is a significant proportion of human carbon dioxide emissions and may increase in the future.

Our research reveals that warmer oceans can ultimately produce more calcium carbonate shells than today’s oceans, even if ocean acidification almost certainly occurs.

How fast nature carbon The potential for sea sequestration to change remains highly uncertain.It will take centuries to reach us Ocean Similar to what was found 4 to 8 million years ago.

To understand how this transition occurs and whether it is possible and wise to increase marine biological productivity to mitigate climate change and maintain or increase biodiversity. , Needs more work.

Antarctic storms cause carbon dioxide outgassing

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The sea has better carbon storage than trees.In a warmer future, marine carbon sinks may help stabilize our planet

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