Researchers have unveiled significant findings about the Patagonian ice sheet, revealing that its history comprises periods of both expansion and contraction rather than a consistent ice-age narrative. That updated story includes the past 120,000 years. Most importantly, it provides new and powerful evidence for climate forcing glacial advance and retreat interactions in the southern hemisphere.
The study highlights how fluctuations in the ice sheet were primarily driven by variations in summer solar radiation and the duration of summer seasons, referred to as “integrated summer energy.” This novel technique uncovers the way ice cover was controlled. It gives researchers new tools for understanding how climate has changed in the past.
Periods of Glacial Advance and Retreat
Second, the Patagonian ice sheet underwent two major glacial advances during the last ice-age cycle. The initial event occurred roughly 71,000 years ago at the onset of marine isotope stage (MIS) 4. The second event, MIS 2/1, took place at the termination of MIS 3—about 35,000 years ago. These advances were uneven. In reality, about 60,000 years ago, the Fennoscandian ice sheet completely melted down.
The research reveals that the advances and retreats of the Patagonian ice sheet were influenced by changes in solar energy received during summers. In particular, variation in integrated summer energy tracked closely with the ice sheet’s development. This correlation hints that climate conditions in this part of the country may have been more intricate than previously realized.
“The aim of our study was to investigate the spatial-temporal history of the Patagonian ice sheet during the entire last glacial cycle—from around 120,000 years ago until today—and thus to gain a better understanding of the causes of the temporal sequences and dynamics of the advances and retreats of the glaciers.” – Andrés Castillo-Llarena
Climate Interactions and Orbital Forcing
The team of researchers noted that while the Patagonian ice sheet’s fluctuations followed a regular cycle aligned with changes in Earth’s tilt angle, short-term climate variations played a crucial role. These millennial-scale fluctuations cannot only be explained by insolation changes, but can be attributed to rapid climate shifts seen in the northern hemisphere. Curiously, maximum glacier advance in the southern hemisphere’s mid-latitudes occurred nearly simultaneously with these advances to the north. Yet, this did not match with the northern glacial history.
Scientists found that the northern and southern Patagonian ice fields are the last of a vastly more extensive former ice sheet. This colossal ice sheet didn’t always rule the surrounding valleys. Over most of the last 2.5 million years, the Central Andes Mountain chain was covered in ice during times of widespread glaciation. This frozen domain extended from 38 to 55 degrees south latitude.
“These findings are of particular significance because there are relatively few data on past climate fluctuations from the southern hemisphere. For a better understanding of future climate change, however, it is important to understand how the northern and southern hemispheres interact with one another.” – Dr. Matthias Prange
Implications for Future Climate Understanding
The national implications of this research go well beyond just understanding where glaciers used to be. The researchers stress the importance of developing a holistic approach to understanding climate dynamics. Their research revealed that incorporated summer energy impacts not only the Patagonian ice sheet, but other mid-latitude ice masses in the SH.
Those interpretations go against previous conjectures made from geological reconstructions that indicated a much more linear glacial history. They illustrate that the interactions between different climatic factors yield complex results that must be carefully studied to predict future changes.
“We suspect that the integrated summer energy modulated not only the behavior of the Patagonian ice sheet, but also that of the other ice masses throughout the mid-latitudes of the southern hemisphere.” – Andrés Castillo-Llarena