The icy depths of the Southern Ocean hold a secret that could spell trouble for continents far away. A recent study published in Nature reveals a surprising link between warming deep-sea waters around Antarctica and rising sea levels in the North Atlantic.
The culprit? A massive system of ocean currents known as the Atlantic Meridional Overturning Circulation (AMOC).
The AMOC acts like a giant conveyor belt, transporting warm surface waters from the tropics northward and cold, dense deep waters southward.
This circulation pattern plays a crucial role in regulating global climate. The warm water masses released by the AMOC help to keep western Europe mild, while the cold, deep waters help to store heat in the ocean depths.
A Weakening Abyss
JUAN BARRETO/AFP via Getty Images
The new study, which analyzed data collected over two decades, has found a disturbing trend: a critical part of the AMOC, known as the abyssal limb, has weakened by 12%. This weakening is caused by a slowdown in the flow of cold, dense Antarctic bottom water (AABW) northward.
The AABW forms around Antarctica as surface waters freeze and become denser. This dense water then sinks and travels along the ocean floor towards the North Atlantic.
The slowdown of the AABW is linked to human-induced environmental changes around Antarctica.
The warming of the atmosphere is causing glaciers to melt and sea ice to retreat, which is disrupting the delicate balance of salt and temperature that drives the formation of AABW.
From South to North: The Ripple Effects of a Changing Ocean
The weakening of the abyssal limb has significant consequences for the AMOC and, ultimately, for sea levels in the North Atlantic.
The slowdown of the AABW reduces the amount of cold, dense water sinking into the deep ocean. This weakens the entire AMOC system, leading to a reduction in the northward transport of warm surface waters.
The reduced northward transport of warm water has a chilling effect on the climate of western Europe. As less heat is delivered by the AMOC, temperatures in the region are expected to decline.
Additionally, the weakening AMOC allows more warm surface water to accumulate in the tropics, which can intensify extreme weather events such as hurricanes.
The slowdown of the AMOC also has a direct impact on sea levels. The warming of deep-sea waters contributes to sea level rise through thermal expansion.
As the ocean warms, it expands in volume, leading to a rise in sea level. The weakening of the AMOC is expected to accelerate this process, as more heat is trapped in the upper layers of the ocean.
The findings of this new study highlight the interconnectedness of our planet's oceans. Changes in the faraway Southern Ocean can have profound consequences for climate and sea levels in regions thousands of miles away.
As we continue to alter our planet's climate, it is crucial to understand these complex ocean circulation patterns and the potential consequences of disrupting them.
It is often referred to as a "conveyor belt" because it transports warm surface waters from the tropics northward and cold, dense deep waters southward.
This continuous loop of moving water helps to distribute heat around the planet, influencing weather patterns and climate in regions far from its origin.
The warm surface waters of the AMOC originate in the tropics, where they are heated by the intense sunlight. These warm waters travel northward, carried by currents such as the Gulf Stream.
As they move northward, the warm waters release heat to the atmosphere, helping to keep western Europe mild and moist.
Meanwhile, in the polar regions, surface waters become cold and dense due to processes like evaporation and sea ice formation. This cold, dense water sinks to the ocean floor, forming the deep limb of the AMOC.
The densest and coldest water masses originate from the Southern Ocean around Antarctica, where they are known as Antarctic Bottom Water (AABW).
The AABW sinks to the bottom of the ocean and spreads northward along the ocean floor. As it travels, the AABW absorbs heat from the surrounding water and seafloor. This heat is eventually released back into the atmosphere in the North Atlantic, helping to moderate the region's climate.
The AMOC is a complex system that is influenced by a variety of factors, including wind patterns, salinity, and temperature. However, human-induced climate change is a growing threat to the stability of the AMOC.
The warming of the atmosphere is causing glaciers to melt and sea ice to retreat, which is disrupting the delicate balance of salt and temperature that drives the formation of deep water in the Southern Ocean. Normally, during winter, sea ice forms around Antarctica. As this sea ice forms, it expels salt through a process called brine rejection.
This saltier, denser water then sinks to the bottom of the ocean, forming the core of the AABW. However, with reduced sea ice formation due to warming temperatures, there is less brine rejection, leading to less dense water sinking. This disrupts the delicate balance in the AMOC, causing the formation of AABW to slow down.
