Posts Tagged ‘glaciers reach bedrock and get thicker’

Ice Age Rhythm Shifts

September 10, 2018

For millions of years mild climate allowed soil to build in Canada and the northern regions of Eurasia.  Plants and animals lived and died and their remains turned into thick layers of top soil.  The uplift of the Himalayan Mountains and the Rocky Mountains and the emergence of a land bridge between the Americas changed climate patterns that then became triggered by the Milankovitch Cycles.  (See: https://en.wikipedia.org/wiki/Milankovitch_cycles)  Ice Ages began to occur during the Pliocene over 3 million years ago.  At first Ice Ages lasted for 40,000 years before cycling into interglacial periods.  But about 950,000 years ago Ice Ages began to last for 100,000 years, and they became more severe.  Scientists found evidence suggesting this is when glaciers began to scrape into bedrock instead of the deep soil built up during the Miocene and early Pliocene.  Whereas glaciers slid over soil during earlier Ice Ages, they instead became stuck in bedrock and grew thicker.  Earlier Ice Sheets repeatedly drove into soil and with each Ice Age stripped the soil until 950,000 years ago it finally reached the bedrock.  The increased size of the glaciers caused an increase in the length and severity of Ice Ages.

Image result for Graph showing increased length of Ice Ages over past 2 million years

Graph showing increased length of Ice Ages.

Image result for glacier scraping into bedrock

Glaciers reached bedrock about 950,000 years ago.  Repeated glacial advances eventually stripped away deep layers of top soil.  Later Ice Ages produced glaciers that got stuck in bedrock and grew thicker.

The evidence for changing Ice Age rhythms comes from deep ocean cores taken from the South Atlantic.  Scientists noticed the sudden influx of isotopes that are more common in the Pacific Ocean in the section of cores dating to 950,000 years ago.  These isotopes of neodymium originate from young volcanic islands located in the Pacific Ocean, and the rock sediment erodes into the ocean and gets carried by currents into the South Atlantic.  Normally, older rocks from coastlines surrounding the North Atlantic Ocean with a different ratio of neodymium isotopes erode and wash into the sea, and they predominate.  But normal ocean circulation shuts down during Ice Ages, and more water from the Pacific Ocean makes its way into the North Atlantic.

Reference:

Vougen, Paul

“Sea Floor Cores Suggest Sticky, Thick Glaciers Caused Mysterious Shift in Ice Age Rhythms”

Science Augusts 22, 2018