Antarctic warming triggers rising North Atlantic sea levels

Deep beneath the icy waters of Antarctica, a silent crisis is brewing. As the Antarctic deep sea warms, it sets off a chain reaction that reaches the far-off waters of the North Atlantic, causing sea levels to rise.

This alarming phenomenon threatens not just marine life but also the millions of people living in coastal areas. This scenario connects distant corners of our planet in ways we are only beginning to understand.

AMOC: Earth’s ocean ‘conveyor belt’

At the heart of this story is the AMOC (Atlantic Meridional Overturning Circulation). This is a complex system of currents within the Atlantic Ocean, acting to transport heat, essential nutrients, and carbon dioxide from the tropics to the higher latitudes.

The AMOC plays a vital role in regulating Earth’s climate on a global scale. It functions much like the various branches of a river system, with different components contributing to its overall flow and direction.

Scientists have been meticulously studying a specific part of the AMOC: the “abyssal limb.” This refers to a current residing thousands of meters below the ocean’s surface, fueled by the formation of Antarctic Bottom Water (ABW).

ABW is an extremely cold and dense water mass that forms around Antarctica under specific conditions. Due to its density, ABW sinks to the ocean floor and flows northwards. It becomes a primary driver of the AMOC’s abyssal limb.

Slowdown in crucial ocean current

Scientists at University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science, and the National Oceanic and Atmospheric Administration’s Atlantic Oceanographic and Meteorological Laboratory have dedicated over twenty years to meticulously tracking this deep, Antarctic-sourced water.

The experts used specialized instruments moored thousands of meters below the surface. The findings are truly chilling: the abyssal limb of the AMOC is weakening. The measured slowdown, approximately 12%, might seem small at first glance. However, it’s crucial to grasp the sheer scale of the AMOC and this deep-ocean flow.

We’re talking about a current system that spans the entire Atlantic basin, moving a volume of water greater than all the world’s rivers combined. A slowdown of even a small percent translates to a massive change in the transport of cold water from the Antarctic towards the North Atlantic.

Antarctic dynamics and warming

During the Antarctic winter, the formation of sea ice plays a vital role. As seawater freezes, the ice structure itself excludes salt, which is concentrated into the surrounding liquid water. This increases both the salinity and density of the unfrozen water, making it significantly heavier.

This newly-formed, extremely dense water, ABW, sinks towards the ocean floor. Driven by its density, ABW becomes the primary fuel for the abyssal limb of the AMOC, initiating a vast northward flow within the Atlantic Ocean basin.

A weaker abyssal limb indicates that less ABW is being formed and transported towards the North Atlantic. This leads to a reduced influx of cold, dense water in those regions, resulting in the gradual warming of the deep North Atlantic.

Thermal expansion is a fundamental physical property of water. As the deep North Atlantic warms, even slightly, the affected water molecules occupy a greater volume.

“The areas affected by this warming spans thousands of miles in the north-south and east-west directions between 4,000- and 6,000-meters of depth,” said William Johns, a co-author and professor of ocean sciences at the Rosenstiel School. “As a result, there is a significant increase in the abyssal ocean heat content, contributing to local sea level rise due to the thermal expansion of the water.”

Impact of Antarctic warming

The threat of rising sea levels is most evident for coastal cities, where flooding and erosion pose an increasing risk to infrastructure and communities. However, the weakening of the AMOC’s abyssal limb has far-reaching consequences that extend well beyond coastal regions.

Stronger storms

The amount of heat stored in the ocean has a direct link to the intensity of tropical storms and hurricanes. Warmer oceans evaporate more readily, providing additional moisture that fuels these powerful weather systems.

The warming of the deep North Atlantic contributes to an overall increase in the ocean’s heat content, which ultimately intensifies these destructive storms.

Shifting ecosystems

Marine organisms have evolved to thrive within specific temperature ranges. Disruptions to these temperature patterns, even in the deep ocean, have cascading effects on marine food webs.

Changes in temperature can impact the distribution of plankton, disrupting the base of the food chain, and impact the migration patterns and reproductive cycles of larger marine species.

The unexpected connection

Changes in the abyssal regions of the ocean might feel far removed from everyday life for many people. However, these changes in Antarctica and the Atlantic highlight a core concept of Earth’s climate system: our planet is an intricately interconnected web. Actions or changes occurring in one region can have far-reaching consequences on a global scale.

Tips to control Antarctic warming

The primary factor driving the changes observed in the Antarctic and the weakening of the AMOC is human-caused climate change.

Greenhouse gas emissions, primarily from burning fossil fuels, trap excess heat within Earth’s atmosphere. This excess heat is absorbed by the oceans, leading to warming trends even in the most remote regions, such as the Antarctic.

Here’s how the responsibility, and power, shift towards personal decisions and collective action:

Be aware

Building a strong knowledge base is essential. Climate change is a complex issue, but reliable sources such as NASA Global Climate Change provide accurate, science-based information about causes, impacts, and potential solutions. Staying informed empowers individuals to make better choices and advocate for informed policy decisions.

Change your habits

Reducing your carbon footprint has multiple benefits. Energy-efficient homes conserve resources and lower bills. Opting for greener transportation methods, such as cycling, public transit, or electric vehicles, directly reduces greenhouse gas emissions. Supporting businesses with sustainable practices sends a clear message that consumers prioritize environmental responsibility.

Vote with your voice

Elected officials are tasked with representing their constituents. Communicating with local, state, and national representatives demonstrates that climate action matters to voters. Supporting candidates whose platforms clearly address climate solutions is crucial.

Spread the word on Antarctic warming

Open dialogue and information sharing within your social circles can have a ripple effect. Discussing climate change, its impacts, and actionable solutions with friends, family, and your broader community builds awareness and encourages collective engagement for climate-conscious decisions.

The story of the AMOC’s abyssal slowdown underscores the web of our planet’s climate systems. It highlights how individual choices, multiplied across billions of people, truly shape the future health of our oceans and the wellbeing of those who rely on them.

The study is published in the journal Nature Geoscience.

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