Thursday, April 23, 2020

Sea Level Rise Ca. 14,650 Years Ago

The Bølling warming event opened the gates from Beringia to North and South America by melting North American glaciers. At this point the Founding population of the Americas rapidly filled it in a mass migration into virgin territory. Across the pond in Europe, this event gave rise to the Mesolithic repopulation of Europe from several Southern refugia. This climate event also caused sea levels to surge in 500 years. As a popular account explains:
Earth's last Glacial Maximum period began around 33,000 years ago, when vast ice sheets covered much of the Northern Hemisphere.  At the time, the Eurasian ice sheet -- which covered much of Scandinavia -- contained approximately three times the amount of frozen water held in the modern-day Greenland ice sheet. 
But rapid regional warming saw the ice sheet collapse over a period of just 500 years, according to authors of the study published in Nature Geoscience.  
Analysing sediment drill cores from the Norwegian Sea, the team found that the ice sheet's collapse contributed to an event known as Meltwater 1A -- a period that saw as much as 25 metres added to global sea levels between 13,500-14,700 years ago. 
Lead author Jo Brendryen from Norway's University of Bergen said the Eurasian ice sheet melt coincided with vast regional temperature swings.  
"Studies of ice cores drilled from the Greenland ice sheet have suggested that the atmosphere above Greenland warmed by up to 14C in a few decades at this time," he told AFP. "We think that this warming was the main driver of the ice sheet collapse." 
While Earth is heating everywhere, parts of the world such as the poles are warming far faster than others. Atmospheric concentrations of planet-warming CO2 were around 240 parts per million at the time, compared with over 415 ppm currently.  
The Greenland ice sheet, which contains enough frozen water to lift global sea levels more than six metres, is currently melting at record rates, losing more than 560 billion tonnes of mass in 2019 alone. Parts of Greenland and Antarctica are now melting six times faster than they were in 1990. 
The study showed that the entire Eurasian ice sheet melted in a matter of a few centuries, adding more than four centimetres to sea levels annually -- around 4.5-7.9 metres in total. 
Ice sheets melting or breaking away as global temperatures rise are subject to what climate scientists term temperature "tipping points". Many researchers fear that the ice sheets in Greenland and West Antarctica will continue to melt even if warming is slowed as carbon emissions are cut.  
"Our research support this idea as the marine based sectors of the Eurasian ice sheet abruptly disappeared and did not grow back," said Brendryen.  
"Where the exact tipping-points are located, both for the past ice sheets and the current ice sheets in Greenland and Antarctica, remain however unknown."
The paper and it's abstract are as follows:

Rapid sea-level rise caused by the collapse of large ice sheets is a threat to human societies. In the last deglacial period, the rate of global sea-level rise peaked at more than 4 cm yr−1 during Meltwater Pulse 1A, which coincided with the Bølling warming event some 14,650 years ago. However, the sources of the meltwater have proven elusive, and the contribution from Eurasian ice sheets has been considered negligible. 
Here, we present a regional carbon-14 calibration curve for the Norwegian Sea and recalibrate marine 14C dates linked to the Eurasian Ice Sheet retreat. We find that marine-based sectors of the Eurasian Ice Sheet collapsed at the Bølling transition and lost an ice volume of 4.5–7.9 m sea-level equivalents (SLE) over 500 years. During peak melting, 3.3–6.7 m SLE of ice was lost, potentially explaining up to half of Meltwater Pulse 1A. A mean meltwater flux of 0.2 Sv over 300 years was injected into the Norwegian Sea and the Arctic Ocean at a time when proxy evidence suggests vigorous Atlantic meridional overturning circulation. Our reconstruction shows that massive marine-based ice sheets can collapse in as little as 300–500 years.
Brendryen, J., Haflidason, H., Yokoyama, Y. et al. "Eurasian Ice Sheet collapse was a major source of Meltwater Pulse 1A 14,600 years ago." Nat. Geosci. (2020). 

Related commentary in the same issue here.


NeilB said...

Dear Andrew there's a big error in the intro blurb: "At this point (14500 y.a) the Founding population of the Americas rapidly filled it in a mass migration into virgin territory."
We both know the Americas had been peopled long before that. There are many sites in N and S America with human occupation way older than that and we both know it! NeilB

andrew said...

The evidence for older sites is quite sketchy.