CO₂ Coalition Substack. Submitted June 3, 2026. 16 p.

The CO2 Enigma in Deep Ocean Currents

Ganapathy Shanmugam, Ph.D.

Introduction

Deep Ocean Currents have been well documented in the World’s Oceans ((Heezen, Hollister and Ruddiman, 1966; Hollister, 1967; Pequegnat et al. 1972; Shepard et al. 1979; Shanmugam, 2016, 2017, 2021). Although there are claims of impact of CO2 on deep ocean currents, there are no published empirical data on measurements of CO2 from specific Deep Ocean Currents, such as 1) Thermohaline Contour Currents, 2) Wind-Driven Bottom Currents, 3) Tidal Bottom Currents, and 4) Baroclinic Currents. The role of CO2 on Ocean Currents remains an enigma. The purpose of this note is to document this disconnect between the climate narrative on CO2 and the absence of empirical data on the concentration of measured CO2 in Ocean Currents.

Atmospheric and Oceanic CO2 Measurements

The Keeling Curve (Fig. 1A) is the gold standard of measurements of atmospheric CO2. In the atmosphere, CO2 is measured as ppm (parts per million). By contrast, CO2 is measured as fugacity in the Oceans (Fig. 1C). The release of Surface Ocean CO₂ Atlas (Mkitarian, 2024) on June 19^th, 2024 revealed that the number of oceanic measurements of the climate change-driving greenhouse gas, carbon dioxide (CO₂), has continued to decrease, following a downward trend since 2018. The number of observations submitted to this annual update is as low as the more limited observing efforts from a decade ago, as seen in the graph below (Fig. 1C).

It must be noted that the atmospheric 1 ppm CO₂ is a mixing ratio (a concentration) (Fig. 1A), while the oceanic 1×10⁶ fCO₂ refers to the effective pressure a real gas exerts when accounting for non‑ideal behavior (Fig. 1C). They measure fundamentally different things. Furthermore, these fugacity of CO2 values do not refer to CO2 in specific type of Ocean Currents.

The Climate-Change Narrative

The thermohaline circulation is central to why the deep ocean is Earth’s largest long—term carbon reservoir. Cold, dense waters at high latitudes sink and carry dissolved gases—including CO₂ and O₂—into the abyss, where they remain isolated from the atmosphere for centuries to millennia. This slow overturning effectively stores atmospheric carbon in the deep ocean. There are published articles that discuss “Shifting winter atmospheric teleconnections to the North Pacific…” (Anderson et al., 2026). Their study shows how freshwater influx into the North Atlantic—a process intensified under CO₂‑driven warming—weakens the Gulf Stream and broader Atlantic Meridional Overturning Circulation (AMOC). It also demonstrates how these circulation changes propagate climate effects as far as Alaska through teleconnections. However, there are no quantitative studies on the impact of CO2 on the behavior of Ocean Currents. In a climate narrative, for example:

Bauer (2019) in an article entitled “Climate Change is weakening the Ocean’s Currents. Here’s why that matters” states that “Likewise, in modern-day oceans, the thermohaline circulation mixes dissolved gases (such as carbon dioxide and oxygen) into the deep ocean. This means that the oceans are able to draw down and store more carbon dioxide from the atmosphere. The deep ocean is the largest reservoir (or storage) for carbon dioxide on Earth. If circulation slows due to warming waters, the churning of the carbon dioxide will slow, which will keep more carbon dioxide in our surface waters and atmosphere. This can lead to increasing ocean acidification, which is very harmful to marine life.”

Mkitarian (2024) notes that “The annual release of the SOCAT data product is crucial to quantifying ocean CO₂ uptake – a critical ecosystem service that naturally removes ~25% of anthropogenic CO₂ from the atmosphere, offsetting the impacts of climate change caused by human-produced greenhouse gases. This absorption of CO₂ by the ocean means that relatively less carbon ends up in the atmosphere, reducing the greenhouse gas “blanket” that surrounds and warms the planet. While this ability of the ocean to act like a carbon-absorbing sponge is critical, it still has negative consequences, like ocean acidification, which can impact marine life and the people who depend on it.”

According to NOAA (2026), the ocean absorbs about 30% of the carbon dioxide (CO₂) that is released in the atmosphere. As levels of atmospheric CO₂ increase from human activity such as burning fossil fuels (e.g., car emissions) and changing land use (e.g., deforestation), the amount of carbon dioxide absorbed by the ocean also increases. When CO₂ is absorbed by seawater, a series of chemical reactions occur resulting in the increased concentration of hydrogen ions. This process has far reaching implications for the ocean and the creatures that live there. But there are no studies of how ocean acidification affects Ocean Currents.

Four Types of Ocean Currents

In an oceanographic context, global circulation of water masses were discussed by Talley (2013) (Fig. 2). In a comprehensive review, Shanmugam (2008) identified four types of bottom currents in the world’s Oceans, namely (1) Thermohaline-Driven Geostrophic Contour currents, (2) Wind-Driven Bottom Currents, (3) Tide-Driven Bottom Currents, and (4) Internal wave/tide-driven baroclinic currents.

1. Thermohaline-Driven Geostrophic Contour currents

In the Atlantic, geostrophic thermohaline contour currents were discussed by Heezen et al. (1966) and by Hollister (1967) (Fig. 3A). The Antarctic Bottom Water (AABW) develops as downslope gravity flows (Fig. 4), but turns into a Contour current with a distinct bottom current layer (Fig. 5). To date, there are no measured CO2 content in the bottom current layers of thermohaline contour currents.

2. Wind-Driven Bottom Currents

The Pliocene-Pleistocene sequence cored in the Ewing Bank Block 826 field in the Gulf of Mexico (Fig. 6) provides an example of sand distribution and reservoir quality of deep-marine bottom-current reworked sands (Shanmugam et al. 1993). Presumably, the Loop Current (Fig. 7), a strong wind-driven surface current in the Gulf of Mexico, impinged on the sea bottom, as it does today, and resulted in bottom-current reworked sands (Fig. 8). To date, there are no measured CO2 content in wind-driven bottom currents with complex hybrid flows (Fig. 9).

3. Tide-Driven Bottom Currents

Submarine canyons provide a unique setting for tidal processes to operate from shallow-marine to deep-marine environments. In modern canyons, current-meter measurements at varying water depths (46–4200 m) show a close correlation between the timing of up- and down-canyon currents and the timing of semi-diurnal tides (Shepard et al. 1979; Shanmugam, 2003)). These tidal bottom currents in submarine canyons commonly attain maximum velocities of 25–50 cm/s (Fig. 10). To date, there are no measured CO2 content in tidal bottom currents in submarine canyons.

4. Internal wave/tide-driven Baroclinic Currents

In a comprehensive review, Shanmugam (2013) discussed oceanographic aspects of baroclinic currents (Figs. 11 to 15). Internal waves are gravity waves that oscillate along oceanic pycnoclines. Internal tides are internal waves with a tidal frequency. Internal solitary waves (i.e., solitons), the most common type, are commonly generated near the shelf edge (100–200 m [328–656 ft] in bathymetry) and in the deep ocean over areas of sea-floor irregularities, such as mid-ocean ridges, seamounts, and guyots. Empirical data from 51 locations in the Atlantic, Pacific, Indian, Arctic, and Antarctic oceans reveal that internal solitary waves travel in packets. Internal waves commonly exhibit (1) higher wave amplitudes (5–50 m [16–164 ft]) than surface waves (<2 m [6.56 ft]), (2) longer wavelengths (0.5–15 km [0.31–9 mi]) than surface waves (100 m [328 ft]), (3) longer wave periods (5–50 min) than surface waves (9–10 s), and (4) higher wave speeds (0.5–2 m s^–1 [1.64–6.56 ft s^–1]) than surface waves (25 cm s^–1 [10 in. s^–1]). Maximum speeds of 48 cm s^–1 (19 in. s^–1) for baroclinic currents were measured on guyots. However, core-based sedimentologic studies of modern sediments emplaced by baroclinic currents on continental slopes, in submarine canyons, and on submarine guyots are lacking. No cogent sedimentologic or seismic criteria exist for distinguishing ancient counterparts. To date, there are no measured CO2 content in baroclinic currents in the world’s oceans.

Concluding Remarks

Although there are four major types of Ocean Currents (Fig. 16), there are no measured concentration values of CO2 from individual types of Ocean Currents.

Atmospheric CO2 is measured in ppm, whereas Oceanographic CO2 is measured in fugacity. The fundamental values of ppm and fugacity are not comparable for the following reasons:

1 ppm of CO₂ in the Atmosphere represents

· A composition of a gas mixture.

· A dimensionless number.

· Independent of pressure.

· Used in atmospheric science and gas sensors.

1×10⁶ fCO₂ in the Oceans represents

· A thermodynamic activity.

· Has units of pressure (atm, bar, Pa).

· Depends on non‑ideal gas behavior.

· Used in chemical equilibrium, solubility, and high—pressure systems.

There is no direct conversion between “1 ppm” and “1 fugacity” because one is a ratio and the other is an effective pressure.

Various problematic aspects of Climate Change are discussed in great detail elsewhere (Shanmugam, 2023, 2024a and b, 2025, 2026).

Acknowledgements

I thank Angela Wheeler, Executive Director of the CO₂ Coalition, for inviting me to submit this article. I am grateful to Jean Shanmugam for her comments.

References

Anderson, L., Finney, B.P. & Baxter, W.B. 2026. Shifting winter atmospheric teleconnections to the North Pacific reconcile Younger-Dryas and Holocene δ¹⁸O signals. Nat Commun 17, 2287 (2026). https://doi.org/10.1038/s41467-026-68841-2

Bauer, J. 2019. Climate Change is weakening the Ocean’s Currents. Here’s why that matters. UF Thompson Earth Systems Institute. University of Florida. Gainesville, Florida. https://www.floridamuseum.ufl.edu/earth-systems/blog/climate-change-is-weakening-the-oceans-currents-heres-why-that-matters/

Flood, R.D., Hollister, C.D., 1974. Current-controlled topography on the continental margin off the eastern United States, in Burke, C.A. In: Drake, C.L. (Ed.), The Geology of Continental Margins. Springer-Verlag, New York, pp. 197-205.

Gill, A.E., 1982. Atmosphere-Ocean Dynamics. International Geophysics Series, vol. 30. Academic Press, An Imprint of Elsevier, San Diego, CA, 662 p.

Gordon, A.L., 2013. Bottom water formation. In: Steele, J.H., Turekian, K.K., Thorpe, S.A. (Eds.), Encyclopedia of Ocean Sciences, second ed. Academic, San Diego, CA, pp. 415-421. ,https://doi.org/10.1016/B978-0-12-409548-9.04019-7..

Heezen, B.C., Hollister, C.D., Ruddiman, W.F., 1966. Shaping of the continental rise by deep geotropic contour currents. Science 152, 502-508.

Hollister, C.D., 1967. Sediment Distribution and Deep Circulation in the Western North Atlantic (Unpublished Ph.D. dissertation). Columbia University, New York, 467 p.

Klein, G.D., 1971. A sedimentary model for determining paleotidal range. Geol. Soc. Am. Bull. 82, 2585-2592.

Lonsdale, P., Nornark, W.R., Newman, W.A., 1972. Sedimentation and erosion on Horizon Guyot. Geol. Soc. Am. Bull. 83, 289-316.

Lovell, J.P.B., and D.A.V. Stow. 1981. Identification of ancient sandy contourites. Geology 9: 347–349.

Mkitarian, J. 2024. Oceanic measurements of carbon dioxide continue to decrease. NOAASurface Ocean CO2 Atlas (SOCAT). https://globalocean.noaa.gov/oceanic-measurements-of-carbon-dioxide-continue-to-decrease-as-reported-in-this-years-ocean-carbon-data-atlas/

NOAA (The U. S. National Oceanic and Atmospheric Administration) (2026). Ocean acidification. NOAA Education. https://www.noaa.gov/education/resource-collections/ocean-coasts/ocean-acidification Accessed June 3, 2026

Pequegnat, W.E., 1972. A deep bottom-current on the Mississippi Cone. In: Capurro, L.R.A., Reid, J.L. (Eds.), Contribution on the Physical Oceanography of the Gulf of Mexico. Texas A&M University Oceanographic Studies, 2. Gulf Publishing, Houston, TX, pp. 65-87.

Purkey, S.G., Smethie, W.M., Gebbie, G., Gordon, A.L., Sonnerup, R.E., Warner, M.J., et al., 2018. A synoptic view of the ventilation and circulation of Antarctic bottom water from chlorofluorocarbons. Annu. Rev. Mar. Sci. 10, 503-527.

Shanmugam, G., 2003. Deep-marine tidal bottom currents and their reworked sands in modern and ancient submarine canyons. Mar. Petrol. Geol. 20, 471-491.

Shanmugam, G., 2008. Deep-water bottom currents and their deposits. Chapter 5. In: Rebesco, M., Camerlenghi, A. (Eds.), Contourites, Developments in Sedimentology, Vol. 60. Elsevier, Amsterdam, pp. 59-81.

Shanmugam, G., 2012. New Perspectives on Deep-Water Sandstones: Origin, Recognition, Initiation, and Reservoir Quality. Handbook of Petroleum Exploration and Production, Volume 9. Elsevier, Amsterdam, 524 p.

Shanmugam, G., 2013. Modern internal waves and internal tides along oceanic pycnoclines: challenges and implications for ancient deep-marine baroclinic sands. AAPG Bull. 97, 767-811.

Shanmugam, G., 2016. The contourite problem. In: Mazumder, R. (Ed.), Sediment Provenance. Elsevier, pp. 183–254.

Shanmugam, G., 2017. Contourites: physical oceanography, process sedimentology, and petroleum geology. Petroleum Exploration and Development. 44 (2), 183-216.

Shanmugam, G. 2021. Mass Transport, Gravity Flows, and Bottom Currents: Downslope and Alongslope Processes and Deposits. Elsevier, Amsterdam. 608 p.

Shanmugam, G. 2023. 200 Years of Fossil Fuels and Climate Change (1900-2100). The Journal of the Geological Society of India, v. 99, 1043-1062.

Shanmugam, G. 2024a. Fossil fuels, climate change, and the vital role of CO2 Plays in Thriving people and plants on planet Earth. Bulletin of the Mineral Research and Exploration, v. 175, 167-208. https://dergi.mta.gov.tr/article/show/2800.html Retrieved October 17, 2023

Shanmugam, G. 2024b. The CO2 Problem: Climate Models vs.Field Measurements. IAS Magazine. 3(2),1-33.

Shanmugam, G. 2025. William Happer, Ph.D. (Princeton): The Consequential Climate Physicist. IAS Magazine, v.4, No. 1, p. 2-48. DOI: https://doi.org/10.51710/jias.v4i1.428

Shanmugam, G., 2026. YouTube Video. The Closure of the Strait of Hormuz and the Obsolescence of Solar Modules. CO2 Coalition Substack. May 7, 2026.

5,55 Mins.

Shanmugam, G., Spalding, T.D., Rofheart, D.H., 1993. Process sediment logy and reservoir quality of deepmarine bottom-current reworked sands (sandy contourites): an example from the Gulf of Mexico. AAPG Bull. 77, 1241-1259.

Shepard, F.P., Marshall, N.F., McLoughlin, P.A., Sullivan, G.G., 1979. Currents in submarine canyons and other sea valleys. AAPG Stud. Geol. 8, 173 p.

St. Laurent, L., Alford, M.H. and Paluszkiewicz, T. 2012, An introduction to the special issue on internal waves: Oceanography, v. 25, no. 2, p. 15–19, doi:10.5670/oceanog.2012.37.

Stow, D.A.V., Hunter, S., Wilkinson, D., Hernández-Molina, F.J., 2008. Chapter 9 The nature of contourite deposition. In: Rebesco, M., Camerlenghi, A. (Eds.), Contourites, 60. Elsevier, Amsterdam, pp. 143-156. Developments in Sedimentology

Talley, L.D., 2013. Closure of the global overturning circulation through the Indian, Pacific, and Southern Oceans: schematics and transports. Oceanography 26 (1), 80-97.

Citation

Shanmugam, G. (2026). The CO2 Enigma in Deep Ocean Currents. CO2 Coalition Substack. June 3, 2026 submitted (preprint). 16 p.

Originally published at Ganapathy Shanmugam, Ph.D. Substack, May 31, 2026.