Scientists have discovered the cause for rapid sea level rise in two specific historic events using climate and ice sheet models. The process, known as saddle-collapse, was at the heart of two specific sea level rise events: the Meltwater pulse 1a (MWP1a) around 14,600 years ago and the ‘8,200 year’ event.
The research, published in the journal Nature, was conducted by Dr Lauren Gregoire of Bristol’s School of Geographical Sciences and colleagues. They studied a climate model and unearthed a series of events that would lead to the saddle-collapse which saw the massive ice sheets over the North American continent separate, in turn leading to rapid melting and the opening of an ice free corridor.
Prior to this study, evidence of the events had been recorded in ocean cores and fossil coral records, but the reason behind the events was unclear and widely debated.
North America was covered by massive ice domes, up to 3 kilometres thick, which formed in regions of high snowfall and higher topography, such as the Rocky Mountains in the west of the continent. These ice domes, linked by the saddles – lower valleys between the domes, made up the massive ice sheets covering the continent.
Towards the end of the last ice age the climate warmed naturally. This started to melt ice at high elevations. As the melt continued, it started reaching the saddle area between the domes. This was the beginning of a vicious cycle in which the melting saddle would decrease in height, reach warmer altitudes, and melt even more rapidly as a result, until the saddle had completely melted away.
It took approximately 500 years for the saddles to disappear entirely until only the ice domes remained.
The melted ice flowed into the oceans leading to rapid sea level rises of 9 m in 500 years during the Meltwater pulse 1a event 14,600 years ago and 2.5 m in the second event, 8,200 years ago.
“We didn’t expect our model to produce such a rapid sea level rise,” Dr Gregoire, lead author of the study said. ” We got really excited when we realised that the events we simulated corresponded to real events!”
In the model, Dr Gregoire found that saddle-collapse could explain a significant amount of the sea level rise observed: “The meltwater pulse produced by the saddle-collapse can explain more than half of the sea level jump observed around 14,600 years ago. The rest probably came from the progressive melting of ice sheets in Europe and Antarctica.”
Understanding our planet’s climatic history is, in and of itself, important. But specifically, understanding the saddle-collapse increases our knowledge of the nature of ice sheets and climate change, which in turn allows further questions to be posed and, hopefully, answered.
Source: University of Bristol