Carbon Cycle

[Richard Rathbone]

Hansen reckons that this type of  mixing is over-represented in current models,  not under-represented. This is an underlying reason he is confident that his modelling is better and IPCC underestimates the level of  warming that will happen as aerosol pollution diminishes. I think it  might be relevant to Atlantic salinity calculations and differing opinions on AMOC stability too.

Continental shelf edges  generate  up/down currents. The Med has a high density of them so is a good place to go if you want to find surface organisms at depth. Its a bad place to go if you want to estimate global effects.

[kassy]

Do you have any link for that? Not seen him discuss this part. If it would be important he would be wrong but i think that you are mixing up things. It´s completely unclear what this find means for climate.

[Richard Rathbone]

Do you have any link for that? Not seen him discuss this part. If it would be important he would be wrong but i think that you are mixing up things. It´s completely unclear what this find means for climate.

Its a common theme of his modelling papers. There's not enough data to independently set ocean mixing parameters, aerosol parameters, and ECS. Consequently uncertainties in them are correlated. He makes this point frequently for ECS and aerosols, but brings in mixing as well when there's a more technically detailed discussion.
I haven't seen him make the link between overmixing in the CMIP ocean models, and their salinity bias in the Atlantic yet, thats my speculation. I might not have noticed it, I haven't gone back and reread them since the recent AMOC stability paper that showed a salinity bias was making the CMIP AMOC too stable. Overmixing would make concentrations too uniform but I've no idea whether this is a significant factor in their salinity bias or not. Its something I'm hoping to see discussed when the second part of Hansen's Pipeline paper gets published.

e.g from Hansen's last email where he gets a lot more technical than he usually does in them.
https://www.columbia.edu/~jeh1/mailings/2024/Hopium.MarchEmail.2024.03.29.pdf

There were two reasons that the GCM modelers did not want to include the full aerosol
forcing in their models. First, many of the oceans in the GCMs tended to mix heat into the
deep ocean too effectively, which meant that the GCM needed a slightly exaggerated forcing
to match observed surface warming. Increased net forcing could be achieved with a smaller
(less negative) aerosol forcing

[kassy]

Drought, soil desiccation cracking, and carbon dioxide emissions: an overlooked feedback loop exacerbating climate change


Soil stores 80 percent of carbon on earth, yet with increasing cycles of drought, that crucial reservoir is cracking and breaking down, releasing even more greenhouse gases creating an amplified feedback loop that could accelerate climate change.

The accuracy of climate models depends on many factors -- greenhouse gas emissions from industrial and transportation activity, farm animal "emissions," urban growth and loss of forests, and solar reflections off snow and ground cover. Natural phenomena like volcanic eruptions also contribute and are incorporated into models.

However, some other natural processes have been overlooked. Farshid Vahedifard, professor and Louis Berger Chair in civil and environmental engineering, points to an important one that lies directly beneath our feet and covers most of our planet above water.

In a study published in Environmental Research Letters, Vahedifard notes that soil stores 80 percent of carbon on Earth, and with increasing cycles and severity of droughts in several regions, that crucial reservoir is cracking and breaking down, releasing even more carbon dioxide and other greenhouse gases into the atmosphere. In fact, it may be creating an amplified feedback loop that could accelerate climate change well beyond current predictions.

"This process has not been sufficiently evaluated in the existing literature or incorporated into models," said Vahedifard. "If we don't consider the interplay of drought, soil desiccation cracking, and CO2 emissions, that could result in significant inaccuracies when modeling and predicting climate change. There are other repercussions as well. Poorer soil health can lead to reduced photosynthesis and lower carbon dioxide uptake, and it can compromise the structural integrity of earthen dams that protect against floods."

...

But soil changes caused by drought could be as significant, if not more significant, than any of those factors. Drought, manifested by long periods of low soil moisture content and high temperature, leads to cracking in fine-grained soils, sometimes extending meters below the surface. The cracks result in more exposure to the air, increased microbial activity and breakdown of organic matter, released carbon dioxide, and loss of nutrients and ability to support plant growth, reducing carbon dioxide sequestering.

The deep cracks expose much older reserves of carbon that had previously been stable and protected. The permeation of air into the soil accelerates the release of not only carbon dioxide from organic matter but also other greenhouse gases like nitrous oxide.

Small animals like earthworms and millipedes that help turn the soil over are also affected by the reduced moisture and increased air exposure, being less able to play active roles in nutrient cycling and soil structure maintenance. That, in turn, increases the likelihood of soil cracking and aeration.

"The amplifying effect of soil carbon feedback loops and its interactions with other loops could carry us across tipping points and lead to even more severe and permanent shifts in climate," said Vahedifard.

more:
https://www.sciencedaily.com/releases/2024/03/240313135541.htm

[kassy]

Study suggests faster decomposition rates in waterways could exacerbate greenhouse gas emissions, threaten biodiversity


Humans may be accelerating the rate at which organic matter decomposes in rivers and streams on a global scale, according to a new study from the University of Georgia, Oakland University and Kent State University.

That could pose a threat to biodiversity in waterways around the world and increase the amount of carbon in Earth's atmosphere, potentially exacerbating climate change.

Published in Science, the study is the first to combine a global experiment and predictive modeling to illustrate how human impacts to waterways may contribute to the global climate crisis.

...

Global warming, urbanization, increased nutrients altering global carbon cycle

Rivers and streams play a key role in the global carbon cycle by storing and decomposing large amounts of leaves, branches and other plant matter.

Typically, the process would go something like this: Leaf falls into river. Bacteria and fungi colonize the leaf. An insect eats the bacteria and fungi, using the carbon stored in the leaf to grow and make more insects. A fish eats the insect.

The study found that this process is changing in areas of the world impacted by humans.

Rivers impacted by urbanization and agriculture are changing how quickly leaf litter decomposes.

And when the process speeds up, that insect doesn't have a chance to absorb the carbon from the leaf. Instead, the carbon is released into the atmosphere, contributing to greenhouse gas pollution and ultimately disrupting the food chain.

"When we think of greenhouse gas emissions, we tend to think of tailpipes and factories," said Scott Tiegs, co-author of the study and a professor of biological sciences at Oakland.

"But a lot of carbon dioxide and methane comes from aquatic ecosystems. This process is natural. But when humans add nutrient pollution like fertilizer to fresh waters and elevate water temperatures, we increase the decomposition rates and direct more CO2 into the atmosphere."

...

https://phys.org/news/2024-05-faster-decomposition-waterways-exacerbate-greenhouse.html

[morganism]

Ocean Floor Topography Found to Significantly Impact Carbon Sequestration

The carbon cycle, a key process regulating Earth's climate, involves the movement of carbon between the atmosphere, oceans, and continents. While volcanic eruptions and human activities release carbon dioxide, forests and oceans absorb it, maintaining a balanced system. Carbon sequestration has become a vital method in combating climate change.

A recent study reveals that the shape and depth of the ocean floor account for up to 50% of the changes in oceanic carbon sequestration depth over the past 80 million years. Previous explanations for these changes were attributed to other factors. It has been established that the ocean, the largest carbon absorber on Earth, controls atmospheric carbon dioxide levels. However, the impact of seafloor topography on the ocean's carbon sequestration ability had been unclear.

"We were able to show, for the first time, that the shape and depth of the ocean floor play major roles in the long-term carbon cycle," said Matthew Bogumil, the paper's lead author and a UCLA doctoral student of earth, planetary, and space sciences.

The long-term carbon cycle operates with various elements over different timescales. One significant element is seafloor bathymetry, which includes the mean depth and shape of the ocean floor. This factor is influenced by the positions of continents and oceans, sea levels, and mantle flow. Carbon cycle models, using paleoclimate datasets, form the basis of our understanding of the global marine carbon cycle and its response to natural disturbances.

"Typically, carbon cycle models over Earth's history consider seafloor bathymetry as either a fixed or a secondary factor," said Tushar Mittal, the paper's co-author and a professor of geosciences at Pennsylvania State University.

Published in Proceedings of the National Academy of Sciences, the study reconstructed bathymetry over the last 80 million years and used a computer model to measure marine carbon sequestration. Results showed that ocean alkalinity, calcite saturation state, and carbonate compensation depth were strongly affected by changes in shallow ocean areas (about 600 meters or less) and the distribution of deeper regions (greater than 1,000 meters). These factors are crucial in understanding how carbon is stored in the ocean floor.

The researchers found that, for the current geologic era, the Cenozoic, bathymetry alone explained 33%-50% of the variation in carbon sequestration. Ignoring bathymetric changes has led researchers to incorrectly attribute changes in carbon sequestration to other factors, such as atmospheric CO2, water column temperature, and silicates and carbonates from rivers.

"Understanding important processes in the long-term carbon cycle can better inform scientists working on marine-based carbon dioxide removal technologies to combat climate change today," Bogumil said. "By studying what nature has done in the past, we can learn more about the possible outcomes and practicality of marine sequestration to mitigate climate change."

This new insight into the influence of ocean floor shape and depth on carbon sequestration also has implications for the search for habitable planets.

"When looking at faraway planets, we currently have a limited set of tools to give us a hint about their potential for habitability," said co-author Carolina Lithgow-Bertelloni, a UCLA professor and department chair of earth, planetary and space sciences. "Now that we understand the important role bathymetry plays in the carbon cycle, we can directly connect the planet's interior evolution to its surface environment when making inferences from JWST observations and understanding planetary habitability in general."

The researchers' work is far from over.

"Now that we know how important bathymetry is in general, we plan to use new simulations and models to better understand how differently shaped ocean floors will specifically affect the carbon cycle and how this has changed over Earth's history, especially the early Earth, when most of the land was underwater," Bogumil said.

https://www.energy-daily.com/reports/Ocean_Floor_Topography_Found_to_Significantly_Impact_Carbon_Sequestration_999.html

https://www.pnas.org/doi/10.1073/pnas.2400232121

[Bruce Steele]

https://www.pnas.org/doi/10.1073/pnas.2400232121

“The shape of the ocean floor (bathymetry) and the overlaying sediments provide the largest carbon sink throughout Earth’s history, supporting ~one to two orders of magnitude more carbon storage than the oceans and atmosphere combined”


How bathymetry affects paleo record of carbon cycle ,calcium compensation depth.
Paywalled, hat tip to morganism.

My guess is the ratio of shallow water and shelf verses deep waters ( below CCD ) affects efficacy of the oceans as sinks.