Meltwater Pulse 1A
Climate Change Daily Earth Science Hydrosphere Repost

Meltwater Pulse 1A

Sea-level rise is an ongoing concern in the low-lying coastal regions of the world. The world’s oceans crept up nine centimeters over the past 25 years. So, this translates to a rate of 36 centimeters (14.2 inches) per 100 years. But documented sea level rise in the past far outpaces this current rate of change. An event known as Meltwater Pulse 1A saw the oceans rise by twelve meters over 400 years, hence a rate of three meters (9.8 feet) per 100 years.

Meltwater Pulse 1A occurred about 14,600 years ago during the waning stages of the last ice age. This period is also the same timeframe for the Missoula Floods that inundated the northwestern USA. Both of these events had their origin in glacial meltwater. 

During the last ice age, thick ice sheets covered much of the northern hemisphere. But the rise in global temperatures as the ice age ended, facilitated the rapid melting of these massive ice sheets. Then quickly melting ice turned into rapidly rising seas. 

Adding up the numbers

A twelve-meter sea-level rise requires a lot of melted ice. Researchers have historically had a difficult time making the numbers add up. However, recent work at the University of Bergen sheds light on a potentially significant contribution to Meltwater Pulse 1A – the Eurasian Ice Sheet. This ice sheet covered Scandinavia and the Barents Sea. Its total volume was about three times greater than the present-day Greenland ice sheet.

Previous research placed the Eurasian Ice Sheet melt before Meltwater Pulse 1A. But the recent research reexamined the timing of the melting and determined that it coincided with Pulse 1A. The previous work assumed that the carbon-14 dates placed on the ice sheet melting included a deep-ocean delay of several hundred years.

This deep-ocean delay relates to the circulation time for deep ocean water. Carbon-14 is continually produced in the atmosphere, but once it leaves the atmosphere, it starts to decay.  Carbon-14 that is used by living organisms or sucked into the deep oceans, immediately starts the decay process. Animals that take up this carbon-14 in the deep ocean and then die, show carbon-14 ages as if they were hundreds of years old, or more. This discrepancy occurs because the carbon they ingested left the atmosphere hundreds of years ago and has already undergone some amount of carbon-14 decay. 

The University of Bergen team correlated the Norwegian Sea sediment records with mineral growth rates in China, getting a more precise understanding of when the Eurasian Ice Sheet melted. The measured mineral growth occurred as annual growth rings in cave stalactites. This correlation was possible because there is a strong correlation between North Atlantic Temperatures and Asian Monsoon rains. The timeline revealed by the cave correlations eliminated the need for a deep-water delay assumption.

Previously researchers attributed one meter of Meltwater Pulse 1A rise to the Eurasian Ice Sheet. But the new research raises that contribution to five meters, thus bringing the total sea-level rise numbers into a better balance.

Implications for today

Meltwater Pulse 1A is historical proof of sea levels rising far more rapidly than we currently experience. The rapidity of the rise directly relates to the rate of ice melt and raises questions about current assumptions of ice melt rates in Antarctica and Greenland. A prediction is only as good as the data and assumptions that go into it. 

Multiple studies today are uncovering new factors that amplify the rate of ice melt. Meltwater Pulse 1A probably started slow but accelerated as feedback loops developed in the melting process. At some tipping point, the melting process then raced on under its own momentum, leading to a twelve-meter sea-level rise in 400 years. Miami and other low-lying megacities hope that the 36-centimeter (14 inches) rise per 100 years is the correct answer, not the three-meter (10 foot) rise per 100 years, as seen in Meltwater Pulse 1A.


Rising seas: Let’s look at the numbers (Source: ArcheanWeb) – Also:

Riding the global conveyor belt (Source: ArcheanWeb) –   Also:

Much ado about tipping points (Source: ArcheanWeb) – Also:


A puzzling past sea level rise might have its missing piece (By Scott K. Johnson; Ars Technica) – Also:

Deglaciation of the Eurasian ice sheet complex (By Henry Patton, Alun Hubbard, Karin Andreassen, Amandine Auriac, Pippa L. Whitehouse, Arjen P. Stroeven, Calvin Shackleton, Monica Winsborrow, Jakob Heyman, Adrian M. Hall; Science Direct) – Also:

Feature Image: Polar Ice (Modified) – By NASA Goddard Space Flight Center from Greenbelt, MD, USA – NASA’s Aerial Survey of Polar Ice Expands Its Arctic Reach, Public Domain,

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.