The Sequestration Efficiency of the Deep Ocean

[Geoengineering News]

‎‎https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025GL116799?af=R

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‎Authors: Benoît Pasquier, Richard J. Matear, Matthew A. Chamberlain, Tilo Ziehn, David K. Hutchinson, François W. Primeau, Yi Liu, Ann Bardin

First published: 23 September 2025

https://doi.org/10.1029/2025GL116799

Abstract

The abyssal ocean may provide adequate sequestration for Carbon Capture and Storage and Carbon Dioxide Removal. The transit of carbon from seafloor release to ocean surface can take millennia, as it occurs through many water pathways characterized by long-tailed transit-time distributions (TTDs). However, multi-millennial simulations of TTDs are typically prohibitively expensive. Here, we introduce an idealized but computationally efficient methodological framework for computing TTDs offline from climate-model archives. We applied this framework to one Earth System Model to estimate the deep ocean sequestration efficiency for the 2030s and 2090s ocean circulations. We found that sequestration is most efficient on abyssal plains isolated from deep branches of the conveyor belt, such as the North Pacific Basins, where less than 10% of the water reaches the surface after 1,000 years. The climate-warming-induced slowdown of the 2090s deep-ocean circulation extends return times by about 30%, which exceeds internal climate variability (~20%).

Plain Language Summary

To limit global warming, we must reduce emissions and actively remove CO2 from the atmosphere. For both Carbon Dioxide Removal and Carbon Storage and Capture at the source, the abyssal ocean may provide adequate long-term storage. This is because dissolved carbon can take up to millennia to travel from the seabed to the surface. We could compute these seabed-to-surface transit times using multi-millennial climate-model simulations, but this is expensive and time-consuming, possibly taking years on powerful supercomputers. To compute these transit times, we introduce a highly efficient method that uses only climate-model archives; that is, without having to run an expensive climate model. While our method is not a perfect substitute for full-climate-model simulations, it allowed us to gain new insights from a wide range of simulations for a substantially smaller fraction of the time and resources. We applied our method to ACCESS-ESM1.5, the Australian climate model, and identified preferred locations for highly efficient sequestration such as the North Pacific Basins, where less than 10% of carbon will return to the surface after 1,000 years. We also found that global warming weakens the deep ocean 2090s circulation and tends to extend sequestration by about 30%.

Key Points

We introduce an idealized but computationally efficient method to estimate transit-time distributions (TTDs) from climate-model archives

In ACCESS-ESM1.5 it takes up to 

 years for 10% of the water on the North Pacific seabed to reach the ocean surface

Under SSP3-7.0 climate change a slower future ocean extends sequestration times by 

30% which exceeds 

20% internal climate variability

Source: AGU

[Bhaskar M V]

Quote from the Paper

"Abstract

The abyssal ocean may provide adequate sequestration for Carbon Capture and Storage and Carbon Dioxide Removal."

The paper does not mention the quantum of natural Carbon sequestered and how much of this is in the Oceans.

The Gross is ~450,000 GtC and 99% of this could be in the Oceans, i.e., ~445,000 GtC.

The increase in CO2 in the atmosphere is ~300 GtC, resulting in increase from 280 ppm to 420 ppm and 

increase in CO2 in Oceans is ~150 GtC, resulting in decrease in pH from 8.2 to 8.1.

So total amount of excess CO2 to be removed is ~450 GtC, 

this is about 0.1% of the Gross Natural Carbon Sequestration in Oceans.  

Regards

Bhaskar

Director

Kadambari Consultants Pvt Ltd

Hyderabad. India

Ph. & WhatsApp : +91 92465 08213

https://www.linkedin.com/in/bhaskarmv/