In a groundbreaking study published in Nature Communications, researchers have uncovered the crucial role that eccentricity, rather than obliquity, played as the main driver of the early Antarctic ice ages. The study, led by Tim E. van Peer and his team from various prestigious institutions, focuses on the dramatic climate shifts that occurred between 28 and 20 million years ago during the Oligo-Miocene Transition. This time period is significant as it was a warmer era than today, with only Antarctic ice sheets existing.
The study meticulously analyzed oxygen isotope data from benthic foraminifera (δ18Ob) collected from International Ocean Drilling Program (IODP) Site U1406, located in the northwest Atlantic Ocean. This site provided an exceptionally high-fidelity record that spans approximately 26.4 to 21.8 million years ago, offering new insights into the planet’s ancient climate.
Eccentricity and obliquity are two of Earth’s astronomical cycles that have historically influenced climate patterns. Eccentricity refers to the shape of Earth’s orbit around the Sun, which varies over a cycle of about 100,000 years, while obliquity is the angle of Earth’s tilt on its axis, which changes over approximately 41,000-year cycles. Previously, both were considered significant in driving ice age cycles, but this study highlights a surprising twist in their roles.
The researchers discovered that eccentricity had a remarkably consistent global imprint on the δ18Ob records during this era, while the obliquity signals were inconsistent between different sites. This finding suggests that eccentricity was the primary pacemaker of ice volume changes, outweighing the impact of obliquity. According to the study, the Antarctic ice ages were characterized by larger, eccentricity-paced cycles that were vulnerable to rapid termination.
These findings challenge previous assumptions about the role of obliquity in ancient climate changes and provide new insights into the mechanisms that maintained early Antarctic ice sheet stability. The study highlights how these ice sheets managed to grow even during polar warming episodes, suggesting a self-stabilizing hysteresis effect. However, the rapid terminations of ice ages indicate that the resistance to melting was weaker than current numerical models predict, sometimes resulting in abrupt changes.
The data from Site U1406 are particularly valuable because they fill a gap in the geological record of the North Atlantic Ocean, a climate-sensitive region where previous data were sparse due to discontinuous coring and hiatuses. This new record offers a benchmark against which other Oligo-Miocene records can be compared, providing fresh perspectives on the astronomical pacing of early Antarctic ice ages.
The study also involved sophisticated methodologies, including the use of well-preserved Cibicidoides mundulus specimens to ensure accurate δ18Ob readings and an astronomically tuned age model independent of the δ18Ob data. This robust approach allowed the researchers to identify three main intervals with distinct climatic imprints within the record, each reflecting significant shifts in the Earth’s glacial and interglacial states.
Related Posts
Reference
van Peer, T.E., Liebrand, D., Taylor, V.E. et al. Eccentricity pacing and rapid termination of the early Antarctic ice ages. Nat Commun 15, 10600 (2024). https://doi.org/10.1038/s41467-024-54186-1
