AddSlideNumber_TestB

VEP9001 - SPECIAL TOPICS VI - Class: 01 (2023.1)

Atlantic Meridional Overturning Circulation (AMOC)

Atlantic Meridional Overturning Circulation (AMOC)

February 9, 2026

Topics

Summary

1. Introduction
2. What is AMOC?
3. How does it work?
4. Duration
5. Is AMOC Slowing Down?
6. Trends
7. What to Expect?
8. Research
9. Images
10. Results
11. Discovery
12. Impacts
13. Conclusions

Introduction

Ocean water is constantly circulated by currents. Tidal currents occur near the coast and are influenced by the sun and moon. Surface currents are influenced by the wind. However, other much slower currents that occur from the surface to the ocean floor are driven by changes in salinity and temperature, a process called thermohaline circulation. These currents are transported in a large "global conveyor belt," which includes the AMOC.

What is the Atlantic Meridional Overturning Circulation (AMOC)?

AMOC is a system of ocean currents that circulates water within the Atlantic Ocean, bringing warm water north and cold water south.

The global conveyor belt, partially shown here, circulates cold deep water and warm surface water around the world. The Atlantic Meridional Overturning Circulation is part of this complex system of global ocean currents. This illustration was captured from a short video produced by NOAA Science on a Sphere.

How does it work?

The circulation process begins when warm water near the surface moves toward the poles (like the Gulf Stream in the North Atlantic), where it cools and forms sea ice. As this ice forms, salt is left behind in the ocean water. Due to the high salt content, the water becomes denser, sinks, and is carried southward in the depths below.

Eventually, the water is pulled back to the surface and warms up in a process called upwelling, completing the cycle.

Fig 1. AMOC in relation to global thermohaline circulation.

The entire AMOC circulation cycle and the global conveyor belt is quite slow. It is estimated that it takes 1,000 years for a parcel (any cubic meter) of water to complete its journey along the belt. Even though the process is slow in itself, there is some evidence that the AMOC is slowing down even further.

Figure 2. Schematic of the Meridional Return Circulation. Image credit: Rick Lumpkin from AOML. NOAA.

Duration

Is AMOC slowing down?

As our climate continues to change, is there a possibility that AMOC will slow down or stop completely? While research shows that it has been weakening over the past century, it remains uncertain whether it will continue to slow down or stop circulating completely.

If AMOC continues to slow down, however, it could have far-reaching climate impacts. For example, if the planet continues to warm, freshwater from melting ice at the poles would shift the rain belt in Southern Africa, causing droughts for millions of people. It would also cause sea level rise along the U.S. East Coast.

The Relationship between United States East Coast Sea Level and the Atlantic Meridional Overturning Circulation: a Review - Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Schematic-of-key-AMOC-related-components-of-the-North-Atlantic-Ocean-modified-from_fig2_335091674

Fig. 3: Schematic of key AMOC-related components of the North Atlantic Ocean (modified from García-Ibáñez et al., 2018).

The image above shows trends observed during the period 1870-2016. Regions showing cooling or below-average warming are shown in blue; regions showing above-average warming are shown in red. Image credit: L. Caesar et al. 2018 (Image courtesy of NOAA) Image credit: L. Caesar et al. 2018.

Trends

Figure 4. The adjacent image shows trends in sea surface temperature in the North Atlantic using the NOAA CM2.6 climate model.

What to Expect?

The analysis published in Nature Climate shows that the collapse of the Atlantic Meridional Circulation causes excess

heat to accumulate in the South Atlantic Ocean, resulting in global atmospheric changes.

Orihuela-Pinto, B., England, M.H. & Taschetto, A.S. Interbasin and interhemispheric impacts of a collapsed Atlantic Overturning Circulation. Nat. Clim. Chang. 12, 558–565 (2022). https://doi.org/10.1038/s41558-022-01380-y

Fig. 5: Schematic of the global climate response to AMOC shutdown.

New research raises concerns that ocean circulation will collapse.

Scientists have long feared that warming could cause a breakdown in ocean circulation in the North Atlantic.

New research has found that the real risk lies in the waters of Antarctica, where melting could disrupt currents in the coming decades, with profound impacts on global climate.

Li, Q., England, M.H., Hogg, A.M. et al. Abyssal ocean overturning slowdown and warming driven by Antarctic meltwater. Nature 615, 841–847 (2023). https://doi.org/10.1038/s41586-023-05762-w

Fig. 6: Discussed article

Fig. 7: Recent and projected changes in bottom water properties of the main disturbance operation.

1. Age (Time)

2. Salinity

3. Temperature

Fig. 8: Recent and projected abyssal warming trends of the main disturbance.

Abyssal ocean circulation is a key component of global meridional circulation, cycling heat, carbon, oxygen, and nutrients throughout the world's ocean.

Fig. 9: Projected global circulation changes by 2050.

The strongest historical trend observed in the abyssal ocean is warming in the high southern latitudes.

Furthermore, attributing changes to specific factors is difficult due to limited measurements and because coupled climate models exhibit biases in the region.

It remains unclear what processes led to this warming and whether this warming is linked to a slowdown in ocean circulation.

Fig. 10: Projected changes in Antarctic Ocean water mass in 2041–2050.

Moreover, future change remains uncertain, with the latest projections from coordinated climate models not accounting for the dynamic melting of the ice sheet.

In the study, a high-resolution transient forced ocean-sea ice model was used to show that, in a high-emission scenario, abyssal warming is expected to accelerate over the next 30 years (by 2050).

Fig. 11: Schematic showing mechanisms for reduced abyssal ventilation by 2050.

The study suggests that the influx of meltwater around Antarctica leads to a contraction of Antarctic Bottom Water (AABW), opening a pathway for warmer Circumpolar Deep Waters to gain greater access to the continental shelf.

1. The reduction in AABW formation

2. Contrast

3. Results

Results in warming and aging of the abyssal ocean, consistent with recent measurements.

Projected wind and thermal forcing have little impact on the properties, age, and volume of AABW.

The critical importance of meltwater from Antarctica in the turnover of the abyssal ocean, with implications for global ocean biogeochemistry and climate that may last for centuries.

Extended Data - Fig. 12. Model of forcing fields for wind, thermal, and meltwater disturbances.

Researchers have found that the collapse of this system would change Earth's climate to a state similar to that generated by La Niña - the negative phase of the El Niño Southern Oscillation.

Massive melting in the North Atlantic

A huge amount of heat would accumulate south of the Equator.

Setting up a permanent La Niña state.

Excess heat over the tropical Atlantic would alter zonal atmospheric circulation, inducing subsiding movements over the Eastern Tropical Pacific.

Discovery

Disrupting deep water formation could make the Southern Hemisphere drier and the Northern Hemisphere wetter.

Oceania

North America

Brazil

Asia and Africa

Eastern Australia would suffer from more rain and flooding.

Southwest United States would experience episodes of drought and much worse wildfire seasons.

Worsening drought in the Horn of Africa and more intense and prolonged monsoon rains in Southeast Asia.

Impacts

Dry conditions in many parts of the world, such as Southern Brazil, while bringing excessive rains to other areas, such as the Northeast coast and the Amazon.

El Niño

La Niña

South America

Typically, El Niños are characterized by anomalies of +0.5°C or more, while La Niñas are characterized by anomalies of -0.5°C or less.

Precipitation Anomalies

Fig. 13. Precipitation Anomalies. (a) El Niño; (b) La Niña; and, South America under the influence of La Niña. Source: NOAA.

Thank you!

Questions?

Behance

LinkedIn

Twitter

https://www.behance.net/ux_germano_costa

https://www.linkedin.com/in/germano-costa-clima/

https://twitter.com/costa_clima