A megasplice of globally distributed benthic δ18O records exposes the different astronomical rhythms of the last 35 million years.

Abstract:

Compilations of worldwide benthic δ¹⁸O records (Zachos et al. 2001, 2008; Cramer et al. 2009) led to a significant improvement of our understanding of changing ocean circulation characteristics in the Cenozoic. However, in these compilations, different isotopic records are accumulated and individual astronomical cycles are not always clearly recognizable. Here, we present a benthic δ¹⁸O megasplice for the last 35 Ma that results from the splicing of 11 globally distributed high-resolution isotope records (>11000 measurements). We carefully correlated these isotope records in their overlapping parts, and slightly revised the original astronomical age models when necessary. The result is a megasplice in which individual astronomical cycles are clearly delineated throughout the last 35 Ma. The main disadvantage is that data from single sites do not reflect whole ocean conditions. Nevertheless, benthic δ¹⁸O records from the deep ocean can be regarded as resembling globally averaged temperature and ice-volume conditions.

Subsequently, the imprint of astronomical climate forcing in the megasplice is displayed in a novel way. We display the response of benthic δ¹⁸O to obliquity and eccentricity-modulated precession for 800-kyr wide time-windows. The δ¹⁸O response in function of obliquity and e·sin(w) allows for an assessment of the relative strength of obliquity and precession. The benthic δ¹⁸O response plot as a function of e·sin(w) and e·cos(w) can be viewed as polar plots of which the azimuth represents the longitude of the perihelion and the distance from the pole represents eccentricity. The month during which the Earth reaches perihelion is indicated at the corresponding azimuth. This novel way of visualizing the astronomical imprint allows us to visualise non-trivial dependencies of climate on the phase and amplitude of astronomical parameters. The supplemented figure displays the differences in δ¹⁸O response between the 100-kyr and the 41-kyr world. However, the constructed megasplice allows for an endless amount of such comparisons. For example, a comparison of the response before and after the Oligocene–Miocene transition shows that it was predominantly the northern hemisphere that drove global climate during the Oligocene, and the southern hemisphere during the Miocene.