What If the Ocean’s Climate-Controlling ‘Conveyor Belt’ Came to a Halt?

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What If the Ocean’s Climate-Controlling ‘Conveyor Belt’ Came to a Halt?‘Live ScienceClimate change dials down Atlantic Ocean heating system‘BBC NewsAtlantic Ocean circulation at weakest point in more than 1500 years‘Science Daily

What If the Ocean’s Climate-Controlling ‘Conveyor Belt’ Came to a Halt?

Freak floods drown buildings, bone-chilling air flash-freezes pedestrians and ice encases the Statue of Liberty. It sounds like a disaster movie, and well, it is: In 2004's "The Day After Tomorrow," the collapse of an ocean current in the North Atlantic sends the world into a whirlwind climate doomsday.

And while that ocean current has not actually collapsed, scientists reporting in two new studies have found that it's weakening, by a lot. In fact, the current hasn't been this sluggish in 1,500 years — a finding that could carry serious (although not disaster-movie serious) repercussions for weather and sea-level rise in locations around the world.

In the Atlantic Ocean, the current known as the Atlantic Meridional Overturning Circulation (AMOC) ferries warm surface waters northward — where the heat is released into the atmosphere — and carries cold water south in the deeper ocean layers, according to the National Oceanic and Atmospheric Administration. Its circulation transports heat around the globe like a conveyor belt, and if its movement were to stop, that heat would not get distributed, and weather havoc could ensue. [Doomsday: 9 Real Ways Earth Could End]

But the AMOC has been getting weaker, and cold, freshwater infusions by the runaway melting of glaciers, sea ice and permafrost are to blame, and the AMOC may weaken even further if temperatures on Earth continue to rise and ice reserves continue to melt, scientists reported in the two studies.

In one study, published yesterday (April 11) in the journal Nature, researchers analyzed ocean sediments in a core sampled off the eastern coast of the U.S., from depths where most of the water originated in the North Atlantic's Labrador Sea. They examined positions of different-size sand grains in the geologic record, to reconstruct how the flow of the currents that carried the grains may have changed over time, said study co-author Delia Oppo, a senior scientist in the geology and geophysics department at the Woods Hole Oceanographic Institution.

Quite a lot has been going on:

Climate change dials down Atlantic Ocean heating system

They say the Atlantic Ocean circulation system is weaker now than it has been for more than 1,000 years – and has changed significantly in the past 150.

The study, in the journal Nature, says it may be a response to increased melting ice and is likely to continue.

Scientists involved in the Atlas project – the largest study of deep Atlantic ecosystems ever undertaken – say the impact will not be of the order played out in the 2004 Hollywood blockbuster The Day After Tomorrow.

But they say changes to the conveyor-belt-like system – also known as the Atlantic Meridional Overturning Circulation (Amoc) – could cool the North Atlantic and north-west Europe and transform some deep-ocean ecosystems.

Scientists believe the pattern is a response to fresh water from melting ice sheets being added to surface ocean water, meaning those surface waters “can’t get very dense and sink”.

Atlantic Ocean circulation at weakest point in more than 1500 years

New research led by University College London (UCL) and Woods Hole Oceanographic Institution (WHOI) provides evidence that a key cog in the global ocean circulation system hasn’t been running at peak strength since the mid-1800s and is currently at its weakest point in the past 1,600 years. If the system continues to weaken, it could disrupt weather patterns from the United States and Europe to the African Sahel, and cause more rapid increase in sea level on the U.S. East Coast.

When it comes to regulating global climate, the circulation of the Atlantic Ocean plays a key role. The constantly moving system of deep-water circulation, sometimes referred to as the Global Ocean Conveyor Belt, sends warm, salty Gulf Stream water to the North Atlantic where it releases heat to the atmosphere and warms Western Europe. The cooler water then sinks to great depths and travels all the way to Antarctica and eventually circulates back up to the Gulf Stream.

“Our study provides the first comprehensive analysis of ocean-based sediment records, demonstrating that this weakening of the Atlantic’s overturning began near the end of the Little Ice Age, a centuries-long cold period that lasted until about 1850,” said Dr. Delia Oppo, a senior scientist with WHOI and co-author of the study which was published in the April 12th issue of Nature.

Lead author Dr. David Thornalley, a senior lecturer at University College London and WHOI adjunct, believes that as the North Atlantic began to warm near the end of the Little Ice Age, freshwater disrupted the system, called the Atlantic Meridional Overturning Circulation (AMOC). Arctic sea ice, and ice sheets and glaciers surrounding the Arctic began to melt, forming a huge natural tap of fresh water that gushed into the North Atlantic. This huge influx of freshwater diluted the surface seawater, making it lighter and less able to sink deep, slowing down the AMOC system.

To investigate the Atlantic circulation in the past, the scientists first examined the size of sediment grains deposited by the deep-sea currents; the larger the grains, the stronger the current. Then, they used a variety of methods to reconstruct near-surface ocean temperatures in regions where temperature is influenced by AMOC strength.

  • Publisher: ScienceDaily
  • Citation: Web link

Watching: What If, Conveyor Belt’ Came, Live Science Climate

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Apr 12th, 2018 04:05 UTC The 2004 film “The Day After Tomorrow” imagined a world in which the complete collapse of a climate-regulating Atlantic Ocean current triggered catastrophic sea-level rise and extreme weather events in the U.S. Credit: Everett Collection Freak floods drown

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