School of Geography - Theses

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Start date: 2020 × End date: 2022 × Type: Masters Research thesis ×

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    The timing of glacial Termination IX in Italian lake sediments: a test of orbital theory
    Port, Corey ( 2022)
    Over the last million years, glacial terminations (transitions between glacial and interglacial periods every 100,000 years) have been driven by changes in the Earth’s orbital parameters. Historically, it was believed that changes in the Earth’s climatic precession paced terminations. A recent assessment of 11 radiometrically dated terminations by Bajo et al. (2020) has instead implicated obliquity as a persistent influence on their initiation and duration, contributing to the wider debate surrounding the relative importance of obliquity and precession in governing ice-age cycles. However, a lack of well-constrained age estimates for the two-remaining Early-Pleistocene terminations (T-VIII and T-IX) hinders the robustness of the obliquity theory. This thesis addresses the timing of T-IX by combining tephra-dated lacustrine calcium carbonate content (%CaCO3), and oxygen stable isotope (δ18O) records from the Sulmona Basin, Central Italy, with a North Atlantic ocean sediment record (from Site U1385, the Iberian Margin) to test this new orbital theory. Here I show that T-IX began at 793.2 ka ±2.5 kyr and ended at 785.5 ka ±3.5 kyr, lasting around 7.7 kyr (which is consistent with the duration of previous terminations). Following a thorough investigation of various orbital parameters and insolation metrics at the start of T-IX, it emerges that T-IX correlates more strongly to a high phase of obliquity than precession. It also began when NH summer insolation intensity was below average, while integrated summer energy was high. Furthermore, the midpoint of T-IX occurs at a peak in the insolation metric of Huybers (2011) (equal amounts of precession and obliquity), consistent with the 11 other terminations. T-IX also occurred two obliquity cycles after T-X, which is consistent with obliquity-paced terminations. As such, T-IX supports Bajo et al. (2020)’s obliquity theory of glacial terminations, challenging previous conceptions of precession-dominated glacial cycles.