Climate response to orbital forcing across the Oligocene-Miocene boundary.
Spectral analyses of an uninterrupted 5.5-million-year (My)-long chronology of late Oligocene-early Miocene climate and ocean carbon chemistry from two deep-sea cores recovered in the western equatorial Atlantic reveal variance concentrated at all Milankovitch frequencies. Exceptional spectral power in climate is recorded at the 406-thousand-year (ky) period eccentricity band over a 3.4-million-year period [20 to 23.4 My ago (Ma)] as well as in the 125- and 95-ky bands over a 1.3-million-year period (21.7 to 23.0 Ma) of suspected low greenhouse gas levels. Moreover, a major transient glaciation at the epoch boundary ( approximately 23 Ma), Mi-1, corresponds with a rare orbital congruence involving obliquity and eccentricity. The anomaly, which consists of low-amplitude variance in obliquity (a node) and a minimum in eccentricity, results in an extended period ( approximately 200 ky) of low seasonality orbits favorable to ice-sheet expansion on Antarctica.
Zachos
J C
JC
Earth Sciences Department, Center for Dynamics and Evolution of the Land-Sea Interface, University of California, Santa Cruz, CA 95064, USA. jzachos@es.ucsc.edu
Shackleton
N J
NJ
Revenaugh
J S
JS
Pälike
H
H
Flower
B P
BP
D000818:Animals; D000864:Antarctic Regions; D001267:Atlantic Ocean; D001272:Atmosphere; D002245:Carbon Dioxide; D002247:Carbon Isotopes / Q000032:analysis*; D002980:Climate; D056890:Eukaryota; D019015:Geologic Sediments; D007053:Ice; D010103:Oxygen Isotopes / Q000032:analysis*; D010933:Plankton; D013057:Spectrum Analysis; D013995:Time
D002247:Carbon Isotopes; D007053:Ice; D010103:Oxygen Isotopes; D002245:Carbon Dioxide