Oceans play a key role in reducing carbon dioxide (CO₂) in the atmosphere and have so far acted as a brake on the full impact of climate change. Current estimates of the loss of atmospheric CO₂ to the ocean, often referred to as the ocean CO₂ sink, indicate that approximately 25% of all human CO₂ emissions are absorbed by the oceans.
In a recent journal article Natural Geology We show that a layer on the ocean surface called “ocean skin,” thinner than a human hair, increases the ocean’s CO₂ absorption by approximately 7%. While it may seem like a small difference, this additional absorption is equivalent to the amount of CO₂ absorbed by the entire Amazon rainforest each year.
This long-term release of carbon into the ocean has negative consequences for ocean health. This is slowly causing ocean acidification; As seawater absorbs more CO₂, this changes the ocean’s chemistry and lowers its pH; This is something that cannot be easily reversed. Since the 1990s, scientists have suggested that cooler skin would increase CO₂ absorption by the oceans. Therefore, CO₂ absorption estimates that ignore this effect will be inaccurate.
Sea surface temperature researchers have since shown that the ocean surface is slightly cooler than the waters just below. This surface crust is on average ~0.17°C cooler. This change in temperature increases the concentration of CO₂ in this tiny particle of water. This is important because it is water that is in direct contact with the atmosphere.
Since CO₂ exchange between the ocean and atmosphere is controlled by the concentration difference between the surface and the water layer below, this colder envelope increases the uptake of CO₂ into the ocean. European researchers confirmed these concentration-based processes in 2007. In the laboratory, they used equipment similar to a powerful microscope with a camera to visualize the oxygen concentration in these tiny layers. In recent years the impact of the surface layer on global carbon in the ocean has been predicted using theory, modeling and satellite observations, but until now no one has actually measured this impact at sea.
To carry out our research, the European Space Agency helped us take special measurements aboard two research ships participating in the annual Atlantic Meridional Transect science cruises, which welcome British and international scientists each year. In 2018, we collected data from our set aboard the Royal Research Ship James Clark Ross, which traveled approximately 9,000 miles (14,500 km) from Harwich in south-east England to Port Stanley in the Falkland Islands.
The equipment was installed on the Royal Research Ship Discovery, which sailed from Southampton, UK, to Puntas Arenas, Chile, in 2019. This ship navigated very rough seas in the North Atlantic and near the Falkland Islands, but saw a mirror-glass ocean near the equator with no real waves, so our measurements represented a wide range of different sea conditions.
Up, up and away?
Two sets of measurements were taken during each flight. For a series of measurements, we used a micrometeorological system to measure wind speed and air temperature along with atmospheric gas measurements. Collectively, this is known as the “eddy covariance system” and tracks how much CO₂ gas in the air moves upward (from the surface) rather than downward. This tells us how much CO₂ is absorbed or released by the ocean.
In the second series of measurements, water samples were collected from the suction pipe on the ship. From this we measured the gas in the water and its temperature. We then combined this with a high-quality thermal imaging camera that measured the skin temperature of the ocean.
If ocean skin had no effect, both sets of measurements together should give the same result. Any differences between the two showed how oceanic skin affects the absorption of CO₂ in the ocean. Accurate estimates of CO₂ absorbed by the oceans are critical in calculating global carbon budgets. These budgets measure how carbon moves through global systems and are used to inform international policies to reduce emissions.
The ocean and the atmosphere are the two main carbon sinks that can be accurately observed. Estimating these accurately constrains all other parts of the global carbon budget and allows us to estimate what is called the “residual budget.” This determines how much more carbon can be released before a particular climate target is reached. More importantly, we cannot estimate the carbon absorbed by all land on Earth without first estimating the carbon absorbed by the oceans. Therefore, a higher ocean CO₂ uptake of approximately 7% would have implications for the entire global carbon budget and the Earth’s capacity to carry greater emissions.
As the UN Climate Summit COP29 in Azerbaijan approaches, this study helps define the CO₂ emissions problem more precisely. Climate experts will need to re-estimate the global carbon budget to reflect our new findings, and this additional ocean uptake will cause an imbalance in the budget, potentially indicating that the terrestrial carbon sink is smaller than currently thought and therefore less effective at removing carbon. atmospheric emissions.
It seems positive that oceans absorb more carbon emissions than previously thought. But the news means that climate change, along with other human activities such as overfishing and pollution, is increasing pressure on the state of the oceans. This may also mean that the capacity of soil to absorb CO₂ is overestimated and that more attention should be paid to protecting ocean ecosystems.
As the need to reduce emissions and meet reduction targets increases, insights into how the ocean skin works will help scientists understand how the ocean responds to our emissions. Unfortunately, this will not set anyone free.
Source: Port Altele
