By Annika Schmidt
Medill Reports

TIERRA DEL FUEGO, Chile — Glacial geologist Brenda Hall clambered up the side of a truck-sized, rain-slicked boulder in clothes soaked from a day hiking over forested ridges in the Patagonian wilderness. Despite heavy, steady raindrops clouding her glasses, Hall used a hammer and chisel to chip into the surface of the massive boulder to collect samples for her research.

It was Hall’s second day in the field at the southern tip of Chile in early March. Joined by field hand and postdoc Rodrigo Soteres, Hall hiked along a peninsula in an unfrequented area called Grandi in search of glacial erratics — boulders left behind by retreating glaciers. The researchers’ drenched rain gear added to the weight of their packs full of gear, including white canvas bags they intended to fill with samples from the boulders.

The only way to navigate and access the formerly glaciated landscapes is via boat, so Hall and a team of scientists spent four weeks aboard the 44-foot sailboat Ocean Tramp. They would sail between field sites and hike into the landscape each day to collect samples.

Hall’s research, which is in the second year of a three-year grant from the National Science Foundation, is part of an ongoing, long-term effort to investigate the mechanism behind rapid global warming. The timing and speed of former glacier melt helps Hall pinpoint, or at least reject, certain hypotheses of the cause of Last Glacial Termination — the period of time where the planet warmed and glaciers retreated. These insights into factors controlling the climate system may help scientists to better understand and predict current and future global warming.

Hall, a professor at the University of Maine, dates rock samples to determine when and how fast the ice sheet in the Cordillera Darwin mountain range retreated over the southern tip of South America. She and a team of five scientists returned to Cordillera Darwin for four weeks in March to support their findings with samples from the landscape at the edges of the former ice sheet. During a prior field season last year, they worked at more central field sites. Comparing deglaciation at the edges to the center is expected to reveal more about the timing and speed of ice melt.

This area was covered by an ice field during the last ice age, and preliminary data from Hall’s research suggest the ice had collapsed back to its center by around 18,000 years ago. However, general understandings from related research suggest the ice sheet was at its maximum, or largest size, not long before 18,000 years ago.

“If we’re right, something really big happened with the climate at that time, which caused rapid warming and ice retreat,” Hall said.

The reserved but indomitable scientist has spent years of her life in the field in Antarctica, the Falkland Islands and Greenland. Hall first went to the Cordillera Darwin mountains in Chile in 2006, and this year marked her sixth field season there. She uses a method called cosmogenic dating to date rock samples back at her lab at the University of Maine in Bangor, Maine. Cosmic rays strike the surface of the boulders and react with quartz to form the isotope beryllium-10, an atomic variation of beryllium with two extra neutrons. Beryllium-10 starts collecting in the rock once it is ice-free and then collects at predictable rates, which can be measured to determine an age of deglaciation.

Despite a slow start on that rainy second day of the field season, the team collected hundreds of pounds of rocks in just four weeks that were shipped back to the Northern Hemisphere and are now undergoing chemical analysis.

“Understanding what factors are controlling climate, especially at the last termination, that’s the most recent kind of abrupt, fast warming that we have. There are other times in the geologic record where that happened even faster, the scale of it was higher, but this is the most recent so that’s where we have the best record,” said Maraina Miles, a postdoc who has worked with Hall for six years.

“(Warming) is off the scales faster, but the systems that were changing at the end of the last ice age, we expect to also be changing now like wind patterns and ocean circulation,” Miles said.

Utilizing boulders as time capsules

At Grandi, it took Hall and Soteres a day and a half to find the first glacial erratic to sample on a narrow coastal peninsula. The strip of land had a steep moraine, an accumulation of soil and rocks left behind by a formerly moving glacier, all along it.

The geologists are dating boulders that glaciers deposited to get an approximate year of the location’s deglaciation. When searching for a viable boulder, Hall is looking for a few things. Ideal boulders are located at the highest points of a moraine ridge, are at least 1 meter tall, do not have surface erosion and contain quartz. But these criteria limit their options, especially in areas with few boulders. She and her team returned to Ocean Tramp with two samples on the second day, but neither boulder was ideal. The first was too small, and the second did not contain much quartz.

“You guys are picky!” said Ocean Tramp captain Ben Tucker, who enthusiastically inquired about the team’s field activities.

The boat crew became invested in the success of each field day — and the more rocks the better. They could feel the weight of the rocks in the scientists’ packs while bringing them back on board at the end of long days on land. Sometimes Tucker would check in on the radio midday, just to see if they had found any samples so far.

The geologists did not know what a site would be like nor how many viable boulders they would find until they were on the ground. “On a satellite image, you can see the landforms, which gives you an idea of where the ice was, but you don’t know when that happened,” Hall said. “Being on the ground, you have a chance of trying to get some chronology.”

Fourteen days after that rainy day at Grandi, Hall and Soteres again hiked into another unknown field site at Whittlebury Island to search for boulders to sample. Ocean Tramp had sailed far west over choppy waters to reach the island, and by late morning, the scientists were on shore hiking up to a ridge of bedrock. The sun was shining, and the scientists’ muscles were stronger after two weeks of hiking and hammering in the field. They shed layers of clothing and took a moment to appreciate the stunning landscape. Small, tree-covered islands dotted the blue sparkling water, and the snow-capped Cordillera Darwin range jutted out from behind some low, light clouds on the horizon.

Whittlebury had many boulders to choose from. When Tucker checked in over the radio in the early afternoon, the geologists already had three samples with a fourth in sight. They ate a lunch of ham and cheese sandwiches on the edge of a ridge, and just offshore below them, a pod of dolphins swam in circles. They could hear the dark gray creatures breathe on the surface of the water. Ocean Tramp was visible on the glistening ocean.

Hall and Soteres each hauled a handful of rock samples back to the boat feeling buoyant about what they had accomplished that day. Hall is particularly interested in the age of these boulders and is prioritizing them back in the lab, since samples can take months to measure the beryllium-10 and generate an age.

Contextualizing research at the end of the world: The history and the challenges

Tierra del Fuego is not an agreeable or easy field site to work. It requires a boat to get around and involves often strenuous hikes over uneven and steep ground, thick with vegetation and prone to unpredictable weather. There were days when the team experienced all four seasons: snow in the morning, clear skies, rain and horizontal hail.

The sunny day at Whittlebury offered a rare treat; the team usually endured drenching rain and blustery winds. On March 17, the team faced ice pellets shooting from the sky horizontally, and wind whipped their jackets furiously as they took their first sample of the day. They collected five samples that day, each in different weather conditions: sometimes rain, sometimes quiet, thick snowflakes with no wind. The team remained soaked all day carrying wet packs weighed down by rocks and rain.

Despite the physical challenges of working in the Cordillera Darwin mountains, little can deter Hall from collecting samples. The payoff is essential. Studying sites at the tip of South America adds context to bigger questions about climate patterns, said Tom Lowell, a co-researcher and geologist who first went to this area of Chile in the late 1980s. Some hypotheses are specific to the Northern Hemisphere, which is influenced by large ice sheets. Research in the Southern Hemisphere can be compared with the Northern Hemisphere to form a broader perspective that considers global climate changes. Lowell’s focus in the field is retrieving core samples from peat bogs that corroborate findings from the cosmogenic science.

Hall abandoned a sample just once this field season when a sudden thunderstorm sent her, Miles and Soteres scampering down an open hillside. Miles was in a T-shirt and writing in her notebook when the trio heard the first clap of thunder. They could see a dark cloud and then wind moving across and flattening the surface of the bay below where Ocean Tramp anchored.

“I opened my pack and put my jacket on because I knew it was going to start raining soon, and slung my pack on and started down the hill, and within 10 steps, it just started raining sideways,” Miles said. “It was like, wham! Out of nowhere.”

The gusts of wind almost blew Miles over as they ran down the hillside. The team still brought back more than a dozen samples that day.

Hall first came to Cordillera Darwin as a student. She worked with Charlie Porter, a renowned climber-turned-climate-scientist who used to own Ocean Tramp and led research expeditions in Patagonia until his death in 2014. His larger-than-life personality and sometimes risky conquests still live on in stories shared in the field or the saloon of his former boat. Hall said Porter’s passion was tangible, but he wanted to constantly be on the move, which sometimes left promising sites unexplored. Today, they’re keeping his legacy alive, conducting research on Ocean Tramp, but “the right way,” Hall said: more structured and thorough.

“You know, if we tried to build the entire case on one season, you would not have as much data as when you keep coming back and keep going back and keep coming back,” Lowell said.

Modern warming and supporting science

Warming today is much faster than it was at the end of the last ice age. Miles said the temperature graph is often described as a hockey stick, with a huge recent spike in global temperature that correlates to the rapid rise in carbon dioxide levels from fossil-fuel emissions, especially since the 1950s. Systems like wind and ocean circulation, which changed at the end of the last ice age, are also expected to also be changing today.

“Answering questions about climate is complicated because climate systems are complicated,” Lowell said.

Hall’s research is on the paleoclimate and what happened thousands of years ago, but modern warming is visible in how the landscape has changed over the past decades. Hall said the ice has recognizably retreated since she first worked in the area in 2006.

“All aspects of our research really have some implications for the current day or future behavior of climate,” Hall said. “The Holocene stuff is interesting because it gives us a sense as to what is normal variability versus what’s not normal. So we’ll have a sense about that, but a lot of our research is looking at the timing of the last termination really gives us an idea of what the mechanisms behind rapid global warming are.”

Collaboration between disciplines may be key to answering questions about climate. While in the field this season, Lowell led the effort to collect peat samples that will be analyzed with radiocarbon dating. The geologists used a core to collect ancient layers of peat from deep in the ground that did not have organic matter in them — indicative of a time when the landscape was covered by a glacier. Dating the first layer of organic matter tells scientists when plants and trees started growing after deglaciation. Radiocarbon dating tracks the predicable decay of the isotope carbon-14 in organic material once a plant or animal dies.

Having dates from radiocarbon dating supports the cosmogenic dates. By using both methods, Lowell explained, scientists can confirm their results when the dates align, or identify discrepancies if they do not. For example, if a boulder from a field site is determined to have been deglaciated 17,000 years ago, and a peat sample shows organic matter starting to grow around the same time, scientists can feel more confident in the accuracy of this date, by using two different methods.

“I definitely think of it as this is a small piece of the puzzle,” Miles said, “but the puzzle is so massive that it’s going to take a lot of effort and a lot of people doing a lot of research to really understand our climate and how it changes and how it’s going to change in the future so we can get prepared a little, hopefully. This type of research goes in to inform models that can then predict what’s going to happen in the future. It’s like a spiderweb. It all meshes together.”

Annika Schmidt is a health, environment and science graduate of the Medill School of Journalism.