Climate Response to Orbital Forcing Across the Oligocene-Miocene Boundary

Abstract

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.

Eocene sedimentary facies in a volcanogenic succession on King George Island, South Shetland Islands: a record of pre-ice sheet terrestrial environments in West Antarctica

“…To gether with re sults of sedimentological and pet ro log ical ob ser va tions, as well as geo chem i cal anal y sis of sed i mentary rocks suc ces sion, it per mits to iden tify three preglacial stages that di rectly pref ace de vel op ment of gla cial con di tions on Ant arc tic con ti nent. These pre-gla cial palaeoclimatic stages (PGS-1-PGS-3) doc u mented cli mate cool ing trends, re corded in ter res trial en vi ron ment that prop erly cor re sponds with global green house-ice house tran si tion, known from ma rine re cord (Zachos et al, 2001(Zachos et al, , 2003(Zachos et al, , 2008.…”

“…This se quence pro vides im por tant de tails that re cord en vi ron men tal con di tions on land dur ing the Early and Mid dle Paleogene, directly pre ced ing ice sheet de vel op ment on the Ant arc tic con tinent. The cli ma tic trend that the suc ces sion re veals can be corre lated with an oce anic re cord of Ant arc tic cli mate evo lu tion based on a com pi la tion of ox y gen iso tope anal y ses and ben thic foraminifera (Zachos et al, 2001(Zachos et al, , 2003(Zachos et al, , 2008.…”

“…Ac tual pat terns of cli mate cool ing dur ing the Late Eocene and the causes of per ma nent and sta ble gla ci ation are still far from be ing un der stood, but there are clues from the sed i mentary re cord of Antarctica that help in ter pret this green house-icehouse tran si tion (Zachos et al, 2001(Zachos et al, , 2003. Geo log i cal ev idence from rocks and fos sils from the Ant arc tic Pen in sula region pro vide sparse clues about cool ing Ce no zoic cli mates in the ter res trial realm (Askin and Spicer, 1995;Dutra, 2001;Fran cis and Poole, 2002;Fran cis et al, 2008).…”

“…Oligocene, di rectly pre ceded gla cial con di tions in Antarctica (Zachos et al, 2001(Zachos et al, , 2003. Ce no zoic global cli mates were gen er ally con trolled by tectonism, that oc curred in south ern mid-to high lat i tudes, cul mi nat ing in the iso la tion of Antarctica, in cep tion of the Ant arc tic Cir cum po lar Cur rent, de vel op ment of the mod ern South ern Ocean, build-up of Ant arc tic ice and de teri o ra tion into ice house con di tions (Ken nett and Baker, 1990 and ref er ences therein; Fran cis et al, 2009;Sijp et al, 2009).…”

Diatom evidence for the onset of Pliocene cooling from AND-1B, McMurdo Sound, Antarctica

“…On geological timescales, polar ice sheets strongly influence regional and global sea level, planetary albedo, continental weathering rates, and ocean and atmospheric chemistry. Each of these factors has the potential to trigger largescale geochemical or physical climate system feedbacks (e.g., Matthews and Poore, 1980;Barron, 1985;Gibbs and Kump, 1994;Zachos et al, 1996Zachos et al, , 2001b. Because the Antarctic system exerts such a dramatic influence on the planet as a whole, understanding how the Antarctic cryosphere responded to warmer climates of the past will provide important constraints in forecasting future climate behavior.…”