Patagonian Ice Holds the Key to Unlocking the Past

A research team recently conducted a study in the Northern Patagonia Ice Field (NPI) to uncover some of the mystery behind Earth’s ancient climate. Along the way, the team made important observations about the current state of glacial ice thinning and climate change.

Through their investigation of ancient paleoclimates (climates prevalent in the geological past), the scientists were able to identify time periods where major glacial growth and decline occurred in the Patagonian Ice Field, contributing important information to our understanding of our planet’s climate following the last ice age. Developing a strong comprehension of glacial advance and retreat over the last 10,000 years in places like the Patagonian Ice Field provides the scientific community with tools to augment our understanding of the past, as the planet’s climate is intrinsically related to its ecology at any given point in our recent geological history.

An astronaut’s photo of a glacier outlet meeting a fjord in the Southern Patagonia Icefield. (Source: NASA)

Patagonia hosts a wide variety of largely untouched landscapes, possessing a range of environments from mountains and deserts to glaciers and grasslands. In addition to its mountainous beauty, the Northern Patagonia Icefield is special in that it is the most glaciated terrain on the planet within its latitude of 46.5 to 47.5 degrees south. The region where the ice field lies is a barren sector of South America spanning nearly 3 million square kilometers across southern Argentina and Chile.

In the glaciated terrain, thick layers of ice and rock hold a wealth of information regarding global climates of the last 25,000 years, offering a glimpse of where we are headed given the recent anthropogenic (human-caused) acceleration of climate change. The study provided scientists with valuable climate data from the Late Pleistocene and Holocene time periods, which began approximately 125,000 years ago following the final episode of widespread global glaciation.

The lead researchers of the study, David Nimick and Daniel McGrath, focused specifically on the the largest outlet glacier draining in the region, the Colonia Glacier on the eastern flank of the ice field. The team sought to constrain the ages of major glacial events by using a variety of dating techniques, including dendrochronology (tree-ring dating), radiocarbon dating, lichenometry (utilizing lichen growth to determine the age of exposed rock) as well as optically stimulated luminescence (dating the last time quartz sediments were exposed to sunlight). Employing such a wide variety of experimental techniques can be a valuable tool in improving the confidence of data and allowed the team to study a diversity of unique properties of the same glacial medium.  

Lichen covered quartz ideal for lichenometry and luminescense. (Source: Tigerente/Wikimedia Commons)

By examining properties of lichen and quartz grains (when they were last exposed to sunlight), the research team was able to  constrain the time at which specific rocks were uncovered from the ice sheets. The age at which the ice melted away to reveal these rocks corresponds to events of retreat (and subsequent advance) of glacial ice across the last few millennia. The determination of major glacial events using these techniques sheds light on the climatic events that not only influenced South American paleoclimate but also may affect present and future glacial retreat given the recent spike in atmospheric carbon dioxide levels.

Results from dating analyses indicated that the most prominent increase in glaciated terrain occurred 13,200 years ago, 11,000 years ago and 4,960 years ago, with the last major advance defining the onset of Neoglaciation – the period of significant cooling during the Holocene or present day epoch. Analysis of a local ice-dammed lake revealed that glacial growth occurred 2,900 years ago and 810 years ago, with ice retreating during the intervening periods. This data points to the idea that in a general sense, warming and cooling even within the last 11,000 year Holocene interglacial period is highly cyclical. Significant Colonia Glacier thinning has been observed since the late 1800’s which has opened up low elevation channels for the local Lago Cachet Dos, a possible reflection of our warming climate and the greenhouse effect.

This knowledge provides an effective framework to which we can compare our actively changing climate. The timing between periods of glacial advance and subsequent retreat are useful metrics for judging the speed at which terrestrial ice is currently disappearing.

Glacial ice melts as it floats in a region north of the NPI. (Source: Adam Derewecki)

Nimick’s team’s findings show advance of the Colonia Glacier occurring approximately every 1,000 years under a climate with generally stable atmospheric carbon dioxide levels. Given the recent benchmark event of passing the 400ppm atmospheric carbon dioxide threshold, it is undeniable that human activity, particularly in the form of carbon emissions, is altering global climate and atmospheric carbon dioxide levels.

As we continue to release more carbon dioxide into the atmosphere, the stable conditions that contributed to the glacial patterns discovered in the study may no longer be present. Increases in greenhouse gases and a warming planet may spell disaster for ice sheets, yet the current speed and extent of glacial melting remain uncertain. Nevertheless, understanding glacial patterns in the Northern Patagonia Ice Field has improved our understanding of paleoclimate following the last ice age and may in fact contribute to our ability to improve forecasts for glacial retreat in the coming years.

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