Description

Why In News?

Researchers from Utrecht University are exploring a dam across the Bering Strait to block fresh water inflow and stabilize the weakening Atlantic Meridional Overturning Circulation (AMOC)

What is Atlantic Meridional Overturning Circulation (AMOC)?

The AMOC is an ocean current system that moves warm tropical surface water northward and returns cold, deep water from the North Atlantic toward the equator.

This circulation regulates global heat, moderating climates in Europe, North America, and equatorial regions.

Mechanism

Warm Water Transport: AMOC moves warm, salty tropical water north, heating regions like Europe.
Cooling & Density: Moving poleward, water cools and mixes with fresh Arctic meltwater, increasing density.
Downwelling: In the North Atlantic, this dense water sinks to deeper layers.
Southward Flow: Cold water travels along the ocean floor as the AMOC's "deep limb," redistributing nutrients.
Resurfacing: The water eventually warms and resurfaces, completing the cycle.

Indian Ocean’s Role: Rapid warming in the Indian Ocean increases local rainfall, drawing air from the Atlantic and reducing its precipitation.

Lower rainfall raises tropical Atlantic salinity.
This saltier water sinks faster as it moves north, jump-starting and intensifying AMOC circulation.

Why is AMOC Weakening?

The primary culprit is Global Warming, which is disrupting the delicate salinity balance of the North Atlantic.

Melting Ice Sheets: Rapid melting of the Greenland Ice Sheet is dumping massive amounts of fresh water into the ocean.
Arctic Sea Ice Loss: Loss of sea ice adds more fresh water.
Result: Fresh water is lighter (less dense) than salt water. This "freshwater hosing" prevents the water from sinking, effectively jamming the conveyor belt.

Implications of AMOC Collapse

Global Impacts

Deep Freeze in Europe: Without the heat transport from the tropics, temperatures in Northwestern Europe could drop by 5°C to 10°C, plunging the region into a deep freeze.
Sea Level Rise: The US East Coast would see a sharp rise in sea levels (up to 1 meter in some models) because the northward current that usually "pulls" water away from the coast would stop.
Amazon Dieback: Rainfall belts would shift, potentially turning the Amazon rainforest into a savannah.

Impact on India

A collapse of AMOC would have a "teleconnection" effect on the Indian Monsoon, primarily by shifting the Inter-Tropical Convergence Zone (ITCZ) southward.

Monsoon Deficit: Recent studies indicate an AMOC collapse could weaken the Indian Summer Monsoon (ISM) rainfall by nearly 20%. (Source: AGU Study 2025)
Erratic Patterns: A 2024 study by IIT Bhubaneswar highlighted that reduced mixing of Atlantic and Arctic waters could disrupt the thermal contrast needed to drive the monsoon winds, leading to frequent droughts.
Winter Warming: Paradoxically, while Europe cools, other parts of the Northern Hemisphere could see erratic warming due to heat piling up in the tropics.

Historical Precedent: The Younger Dryas Event

About 12,900 years ago, a massive glacial lake (Lake Agassiz) burst, flooding the North Atlantic with fresh water.

Result: The AMOC shut down effectively.
Impact: The Northern Hemisphere plunged back into near-glacial cold conditions for about 1,200 years, a period known as the Younger Dryas.

Source: DOWNTOEARTH

Attempt Daily Quiz

PRACTICE QUESTION

Q. Consider the following statements regarding the Atlantic Meridional Overturning Circulation (AMOC):

1. It continuously transports warm, salty surface waters from the northern latitudes to the tropics.

2. The influx of fresh water from melting polar ice sheets increases the density of surface water, accelerating the AMOC.

Which of the statements given above is/are correct?

a) 1 only

b) 2 only

c) Both 1 and 2

d) Neither 1 nor 2

Answer: d

Explanation:

Statement 1 is incorrect: The AMOC transports warm, salty surface waters from the tropics/equator towards the northern latitudes/pole (not from northern latitudes to the tropics).

Statement 2 is incorrect: The influx of fresh water from melting polar ice sheets decreases (not increases) the density of surface water, which inhibits the sinking process and causes the AMOC to weaken or slow down (not accelerate).

Frequently Asked Questions (FAQs)

The AMOC (Atlantic Meridional Overturning Circulation) is a massive system of ocean currents driven by differences in temperature and salt content (thermohaline circulation). It acts as a global conveyor belt, transporting warm surface water from the tropics to the North Atlantic, where it cools, sinks, and flows southward.

Global warming accelerates the melting of polar ice sheets, such as the Greenland ice sheet. This dumps massive amounts of fresh, less dense water into the North Atlantic. This freshwater prevents the surface water from sinking (downwelling), choking the circulation and slowing down the AMOC.

The AMOC helps regulate the global climate and maintains the normal position of the Intertropical Convergence Zone (ITCZ). A weakening or collapse of the AMOC would force the ITCZ southward, which would severely weaken the Indian Summer Monsoon, leading to droughts and agricultural crises.