The Land of Fire and Ice: Investigating the End of the Last Ice Age in Tierra del Fuego, Chile
What causes ice ages? Better yet, what causes them to end so suddenly? Over the last million years, ice ages have happened in roughly 100,000-year cycles. However, the earth spent most of each cycle slowly cooling into the frigid temperatures of a glacial maximum. Then suddenly, in the geologic blink of an eye, the earth warmed up and jumped out of an ice age within a few thousand years. What caused this rapid change? The first step in answering this question is to get a clearer picture of how the climate changed. When and how quickly did it warm up? Did it warm up at the same time everywhere? Answers to these questions can help us get a better idea of how the climate system will respond in the future.
In March of 2023, our team from the University of Maine, the University of Cincinnati, the Universidad de Chile, and the Universidad de Magallanes went to Tierra del Fuego, Chile, to start answering these questions. We lived on a 66’ sailboat for a month and sailed to remote locations along the Beagle Channel to conduct fieldwork. Our goal was to study when and how quickly the glaciers that once covered all of Tierra del Fuego melted back to their current, much smaller sizes during the end of the ice age.
To construct a timeline for glacier retreat, we used multiple types of geologic dating. The first, pictured to the left of this panel, is called, ‘cosmogenic exposure-age dating.’ This method works like a clock that starts ticking as soon as the ice melts away and exposes a rock. By measuring the amount of a certain isotope (10Be) within the rock – produced only when a surface is exposed to the sky – we can date how long it has been exposed to the atmosphere and therefore how long it has been since the ice melted.
Tierra del Fuego is an archipelago at the southern tip of South America. Our field area is highlighted in red.An outlet glacier of the Cloue Ice Field flows out of the mountains. We hiked to this glacier to collect wood fragments for radiocarbon dating.A precariously perched glacial erratic boulder balances in front of Fouque Glacier.Dr. Brenda Hall (red coat) and undergraduate student Eva Griffiths inspect a prospective boulder to sample.Dr. Rodrigo Soteres (right) and Dr. Brenda Hall write field notes for a sample taken from a glacial erratic boulder pictured with the hammer and chisel used to collect the sample.Dr. Rodrigo Soteres uses a rock drill to collect a sample for cosmogenic exposure age dating.Dr. Brenda Hall and Dr. Rodrigo Soteres examine a sample taken from a glacial erratic boulder on a moraine ridge.Pairs of Magellanic cormorants pose for photos from their nests along the cliffs.An Andean condor surveys our fieldwork, wondering if we are food.A black-crowned night heron perches on the side of a boat. Puerto Williams, Chile.A curious buff-winged cinclodes watches us prepare for fieldwork.Sea lions lounge along the coast.Sunset at the harbor in Puerto Williams, Chile.Left to right: Undergraduate student Eva Griffiths, Dr. Tom Lowell, and graduate student Meghan Spoth collect a core from a bog near Fouque sound.Dr. Tom Lowell, Eva Griffiths, and Dr. Rodrigo Soteres carry the successfully extracted core to the staging area where the core will be extruded and packaged for transport.Using a tripod as leverage, Dr. Tom Lowell, Eva Griffiths, and Dr. Rodrigo Soteres extract a core from a bog.Dr. Tom Lowell, Kala Hunter, and Meghan Spoth trudge through the snow carrying coring equipment. On any given day our team of six carried roughly 150lbs of sampling gear into the field.Left to right: Kala Hunter, Eva Griffiths, and Dr. Tom Lowell probe the depths of a bog to find the best place to extract a core. This terrain was once completely covered by glaciers.Dr. Tom Lowell carries a probe rod which we use to find the deepest parts of the bog. Eva Griffiths collects notes on the depths of the bog.
Along with sampling rocks for cosmogenic exposure-age dating, we also dated organic matter with radiocarbon. All organisms absorb carbon, including radiocarbon, while living. Once an organism dies, radioactive decay of the radiocarbon is no longer balanced by uptake, and thus the amount decreases over time. By measuring how much radiocarbon is left, we can get an age for how long ago that organism died. As shown in the pictures throughout this exhibit, Tierra del Fuego is a land with lots of bogs. These bogs formed shortly after the retreat of the glaciers that covered the landscape. By coring down through these bogs to the very base and dating the bottom-most organic matter, or the first plants to colonize the landscape, we can learn when the area first became ice free.
Another way we use radiocarbon is to date fragments of wood that are currently melting out of glaciers. These wood bits were once part of a forest that was overrun by an advancing glacier in the past. This age can tell us when the ice was smaller than present and when it began to advance.
Dr. Brenda Hall, Dr. Tom Lowell, and Meghan Spoth venture towards Fouque Glacier to find pieces of wood that have melted out of the ice.A subglacial channel drains the meltwater of Romanche Glacier along the Beagle Channel.An Andean condor surveys our fieldwork from a distance.Dr. Tom Lowell and graduate student Meghan Spoth battle high winds and sleet on our way to the glacier in the background to collect wood fragments for radiocarbon dating.A seabird takes off as we drop anchor in Caleta Olla, a protected cove along the Beagle Channel.Sunset at the Micalvi Yacht Club in Puerto Williams, Chile. The Dientes de Navarino mountain range provides the backdrop.The characteristic landscape of Tierra del Fuego.Our home for a month was the Ocean Tramp, a 66-foot sailboat. On this snowy day we anchored Caleta Helena Maria.Fall foliage of Nothofagus antarctica, a type of southern beech tree, along the Beagle Channel.Waterfalls fed by the Cloue Ice Field.Undergraduate student Eva Griffiths surveys the edge of Fouque Glacier.The entrance to Pia fjord with the Oblicuó ice cap covering the top of the mountain.A snowy day on the boat.
