Climate Change Daily Earth Science Repost

Oceanic carbon sequestration: good and bad

Removal of carbon from the atmosphere (carbon sequestration) helps counteract the effects of greenhouse gas emissions from fossil fuels. In this sense, carbon sequestration is a valuable natural process. Natural pathways for carbon sequestration include both terrestrial and oceanic processes. However, the removal of carbon (primarily carbon dioxide – CO2) from the atmosphere through absorption into ocean waters has adverse effects on marine ecosystems. So, oceanic carbon sequestration is simultaneously both helpful and harmful. 

A rough breakout of the budget for global CO2 emissions includes a 30% uptake by the oceans, a 25% uptake by the land (plants/soils), and 45% absorption into the atmosphere. Therefore, increases in carbon sequestration will result in a reduction of atmospheric carbon and a slowing of the rate of global warming. But there is “no free lunch.”

Oceans are an essential part of the carbon cycle

The oceans constitute a vast carbon reservoir and the most significant carbon sink on earth. But, is that a help or hindrance to the environment? Ocean acidification, as atmospheric CO2 increases, poses direct threats to marine ecosystems.

Carbonate buffering is the name given to the CO2 exchange process between the atmosphere and the oceans. When CO2 enters the sea, it reacts with water to form carbonic acid, and this causes ocean acidification.

Buffering is a reversible set of chemical reactions. As atmospheric CO2 increases, the oceans become more acidic (lower pH). If atmospheric CO2 drops, then the sea reverses this reaction and returns CO2 to the atmosphere. The earth’s oceans hold about 93% of the CO2 reserves at the surface of the planet, so their role in regulating atmospheric CO2 is critical. But this help comes at a price.

Lower pH sea waters have an adverse effect on creatures that form their shells by extracting chemicals from the ocean. Calcium carbonate is one of these critical chemicals, and as pH lowers, there is less calcium carbonate available for shell formation. This phenomenon threatens the microscopic end of the marine ecosystem – phytoplankton.

The threat to calcareous phytoplankton is a threat to the lowest trophic level of the marine food chain. Reduced ability to build their shells stresses the species. If the phytoplankton populations collapse, then the food chain collapses, thus leading to species decline or extinction higher up the chain. 

High rates of species loss in the last 100 years point to an Anthropocene extinction event that is related to climate change. Acidification of the oceans only exacerbates the species extinction problem. The sequestration of CO2 should be viewed as an environmental issue, not just an atmospheric problem. Greenhouse gas emissions have a knock-on effect across all environmental and ecological processes.  

 Climate change alters an interconnected environment

Popular news often focuses on the immediate and visible aspects of climate change that affect human populations. That is natural since we all want to understand what change means to us personally. However, we should not neglect the growing amount of scientific research that looks at how climate change affects all aspects of our environment.

The earth’s biosphere, atmosphere, hydrosphere, and geosphere are all connected to create this thing we call our environment. Change in one of these sectors inevitably leads to change throughout the whole environmental system. 


Ocean Acidification (Source: ArcheanWeb) – Also:

Acid and phytoplankton in the ocean’s food chain (Source: ArcheanWeb) – Also:


What is carbonate buffering? (John Brennan –  Sciencing) – Also:

What is happening in the ocean (NASA Climate Kids) – Also:

Ocean-Atmosphere CO2 Exchange (NOAA – Science on a Sphere) – Also:

Ocean Food Chain (By Amanda Robb – – Also:

Aquatic food webs (NOAA – National Oceanic and Atmospheric Administration) – Also:

What are phytoplankton? (NOAA – National Oceanic and Atmospheric Administration) – Also:

Feature Photo: Unhealthy pteropod showing effects of ocean acidification (NOAA) (Modified) –  –  This file is licensed under the Creative Commons Attribution 2.0 Generic license. –

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.