Emily Davies explores the revelations of a new study about how much CO2 the ocean absorbs.
Photo by Thach Tran
Until recently, it was believed that the oceans absorbed 25% of all CO2 emissions. A Nature Communications study has revealed they actually absorb twice as much — having significant implications. As the ocean has been removing more emissions from the atmosphere than previously thought, this means one of two things: either our CO2 emissions are much higher than we thought, or the carbon sinks on land (like plants and soil) are much smaller than scientists previously believed.
The study discovered that the skin of the ocean (the very top layer) is colder than water a few meters deeper, changing previous estimates of carbon capture. Oceans cover 70% of Earth’s surface and were already known to be one of the world’s largest carbon sinks, but this study means the oceans are an even larger sink and are working much harder than we thought. The world’s oceans absorb CO2 emissions and drastically slow the global warming process; however, this comes with the cost of changing the water’s chemistry.
So, what is a carbon sink, exactly? Put simply, a carbon sink takes carbon dioxide from the atmosphere and stores it. There are both natural and artificial variants, but the largest sinks are natural, like plants, soil and the oceans.
An example would be forests, which extract carbon from the atmosphere through photosynthesis; for this reason, deforestation is depriving the planet of natural carbon extraction. Over the span of 40 years, a Europe-sized amount of forest has been cut down.
Combined, all of the natural carbon sinks only absorb 50% of all human CO2 emissions at their current level, as — through burning fossil fuels like coal — we have gone way over what they can handle.
How Oceans Store CO2
On the surface of oceans live microscopic algae called phytoplankton. They take in CO2 and release oxygen, and when they die, they become biological debris called ‘marine snow’. Marine snow consistently falls from the surface down to the deep sea, taking nutrients to the seafloor. This is called the biological pump. As the marine snow brings carbon down from the surface to store in the deep sea, the surface can then collect new carbon from the atmosphere.
This study published by NOAA found that as CO2 emissions have increased, the ocean has absorbed more emissions to try and keep up. In the pre-industrial era, the oceans were actually a source of CO2, but have been forced to absorb mass amounts to slow down global warming, acting like a sponge in a quickly filling swimming pool. This doesn’t come freely.
By taking in so much CO2, our oceans are becoming more acidic. A more acidic ocean negatively affects coral reefs and marine life like fish, which in turn affects the coastal economy and food security.
The ocean around Antarctica, in particular, effects the global warming process significantly. This is because the ocean is a key connector between the deep sea and the atmosphere in transferring heat and carbon.
Deep sea water rises to the surface and brings calcium carbonate with it. This then dissolves and makes the ocean water more alkaline, subsequently raising the ocean’s capability of coping with the increasing CO2 levels. From the Southern Ocean, either currents can drag this alkaline water north, or plankton in the Southern Ocean can capture it to make protective shells, keeping it in this ocean. The activity of plankton in this one ocean has the potential to affect global warming, according to Phys Org.
So, oceans are picking up the slack even more than we thought. Our reliance on damaging fossil fuels has forced the world’s oceans to work in overdrive, and whilst we know this, it is broadly overlooked.
How long can the oceans continue to desperately scramble to reduce our contribution to global warming? As the seas become more and more acidic, the coral reefs will die and soon after, many marine species will too. However, recent promising strides in renewable energy will hopefully lead to a drastic decline in fossil fuels and reduce the destruction of marine ecosystems.
Article on a similar topic: Coral Reef Discovered in Australian Ocean
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