The stability of the Atlantic Meridional Overturning Circulation (AMOC) has shown signs of faltering in recent years, possibly leading to major impacts on global climate. However, a recent study suggests an interconnection with the warming Indian Ocean that may give AMOC a boost.
Atlantic Meridional Overturning Circulation: An Overview
Often referred to as the “Atlantic conveyor belt,” the Atlantic meridional overturning circulation (AMOC) is one of Earth’s most extensive water circulation systems. In this system, warm, salty water travels from tropical regions to areas located further north, including western Europe. The system also directs colder water southwards.
As the warm water journeys towards the northern regions, it cools down while its salt content amplifies due to evaporation. The combination of low temperature and high salinity increases the water’s density, causing it to sink deep into the ocean. This cold, dense water slowly traverses southward beneath the ocean surface. Eventually, it resurfaces, warms up again, and the circulation sequence is complete. This ongoing cycle contributes to the continual mixing of the oceans and regulates the distribution of heat and energy across the planet, thereby influencing global climate.
Indian Ocean Warming and Its Impact on AMOC
The rising temperatures in the Indian Ocean may counteract the potential slowdown of AMOC. The warmth in the Indian Ocean leads to heightened precipitation levels, which in turn attracts more air from different parts of the globe, including the Atlantic. Given the increased precipitation in the Indian Ocean, the Atlantic experiences less rainfall, resulting in higher salinity in its tropical waters due to the decreased dilution by rainwater.
This saltier Atlantic water, transported northwards via AMOC, cools and sinks faster than usual. This phenomenon can act as a catalyst for AMOC, enhancing the circulation. However, this boost may cease if other tropical oceans, particularly the Pacific, start to warm up at a rate comparable to the Indian Ocean.
El Niño-Southern Oscillation (ENSO) and Its Role
Alternating oceanic system patterns such as ENSO also have significant effects on rainfall distribution in the tropics and the weather in other parts of the world. ENSO includes temperature changes of 1°-3°C in the central and eastern tropical Pacific Ocean, occurring over periods between three and seven years. El Niño alludes to the warming of the ocean surface, La Niña to cooling, while “Neutral” lies within these two extremes.
| Oceanic Phenomenon | Temperature Change |
|---|---|
| El Niño | Warming of Ocean surface |
| La Niña | Cooling of Ocean surface |
| Neutral | Between Warming and Cooling |
Uncertainties and Historical Implications
Notably, it remains unclear whether the observed slowdown of AMOC results from global warming alone or is just a short-term anomaly correlated with natural ocean variability. Historical records indicate a similar slowdown of AMOC occurred around 15,000 to 17,000 years ago, causing severe winters in Europe and alteration in the location of the tropical rain belt, resulting in more storms or a drier Sahel in Africa.
