Determining Driving Mechanisms of the Last Ice-Age Termination in South America

Expedition Location:  Cordillera Darwin, Chile

Expedition Dates:  March 1 – April 7, 2024

Field Team Members:  Sera Thomas (MS Student, UMaine), Meghan Spoth (Phd Student, UMaine), Maraina Miles (Phd Student, UMaine), Annika Schmidt (MS Student, Northwestern University), Dr. Rodrigo Sotores (Postdoc, University of Magallanes), Dr. Brenda Hall (Co-PI, UMaine), Dr. Thomas Lowell (Co-PI, University of Cincinnati)

Funding Support:  Dan & Betty Churchill Exploration Fund


Research Background:  What drives global climate change? This question is becoming increasingly important as Earth’s atmosphere warms and global sea levels rise. A good way to investigate this problem starts with understanding the causes for ice-age terminations. It’s long been thought that changes in northern hemisphere summer insolation are responsible for causing ice ages (Karner et al., 2000). This mechanism suggests that climate change is controlled by Earth’s orbital patterns: eccentricity, tilt, and precession (Hays et al., 1976), with terminations occurring when these three parameters combine to cause northern hemisphere summer warming. According to this theory, ice ages and their terminations should be out of phase. However, growing evidence shows that the opposite is true – ice ages and their terminations are synchronous between the northern and southern hemispheres. This problem has been dubbed Mercer’s Paradox (Denton et al., 2021). This leads to the question, exactly what caused the termination of the last ice age? I aim to address this question by reconstructing the rate and timing of the last termination in southernmost South America using 10Be surface exposure dates on moraines and glacial erratics.

Study Site:  Field work was conducted in Cordillera Darwin (54.5°S, 70°W), seen in Figure 1 (left), a mountain range in the southernmost part of Chile. This is the only significant landmass at this latitude and lies within the current path of the westerly wind belt, which is thought to play an important role in ice-age terminations. The Penhoat fjord (Figure 1, right) is particularly important because there is a series of well-defined moraines that give a detailed record of the timing and structure of the last termination.

Methods: Our team spent four weeks traversing the north and south arms of the Beagle Channel, visiting several field locations for sample collection. The field season encompassed several sites within the Darwin range as part of a larger project at UMaine that involves not only my research but that of other graduate students (e.g., Meghan Spoth) on the trip. Thirty-three new rock samples were collected at my field site, Penhoat. These samples will be used to obtain 10Be surface exposure dates. In the summer and fall of 2024, I will prepare samples at the University of Maine Cosmogenic Isotope Laboratory. Samples will then be analyzed at the Center for Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory. The data derived from the samples will show when ice retreated from the area. This information will give a better insight into how the last ice-age termination transpired and which mechanisms force global climate change.

Acknowledgements: This Master’s research is facilitated by several sources. First and foremost, I am grateful to my field team members. The completion of this successful field season would not have been possible without their unwavering dedication and perseverance in nonideal weather conditions. Funding for this remote field work was generously provided by the Dan and Betty Churchill Exploration Fund and the University of Maine Graduate Student Grant. I am also indebted to the wonderful captain, Ben Tucker, and crew members of the Ocean Tramp vessel.


Denton, G.H., Putnam, A.E., Russell, J.L., Barrel, D.J.A., Schaefer, J.M., Kaplan, M.R., Strand, P.D. 2021. “The Zealandia Switch: Ice age climate shifts viewed from Southern Hemisphere moraines.” Quaternary Science Reviews 257: 1-28.

Hays, J.D., Imbrie, J., and Shackleton, N.J. 1976. “Variations in Earth’s Orbit: Pacemaker of the Ice Ages.” Science 194 (4270): 1121-1132.

Karner, D.B. and Muller, R.A. 2000. “A Causality Problem for Milankovitch.” Science 288 (5474): 2143-2144.




Google maps identifying site location.
Figure 1. Left: Location of Cordillera Darwin in context of the Southern Hemisphere Westerlies. Right: Penhoat region location.


Photo of field team member Meghan Spoth hiking.
Photo courtesy: Maraina MilesFigure 2. Meghan Spoth in foreground hiking in Tierra del Fuego. Above on ridge, Rodrigo Sotores and Annika Schmidt sampling bedrock for 10Be surface exposure dating.


Figure 3. A view from shore at Penhoat fjord.


Field team member R. Sotores using a hammer and chisel to collect samples.
Photo courtesy: Maraina Miles.Figure 4. Dr. Rodrigo Sotores using hammer and chisel to collect samples from a glacial erratic for 10Be surface exposure dating.


Group photo of field team on board the Ocean Tramp.
Figure 5. Scientists, reporter, and crew on board the Ocean Tramp.


Photo of erratic boulders at Penhoat fjord.
Photo courtesy: Maraina Miles.Figure 6. Erratic boulders at Penhoat fjord.


Photo of the Ocean Tramp boat.
Figure 7. The Ocean Tramp.