georefid:2003-038186SEDIS Publication Catalogue

ana.macario@awi.de

http://sedis.iodp.org/pub-catalogue/informationpointOfContact2011-06-23T00:00:00Zhttp://sedis.iodp.org/pub-catalogue/index.php?id=2003-0381862001-01-01publicationgeorefid:2003-038186Zachos, James C.University of California at Santa Cruz, Department of Earth Sciences, Santa Cruz, CA, United StatesauthorShackleton, Nicholas J.Cambridge University, United KingdomauthorRevenaugh, Justin S.University of South Florida, United StatesauthorPalike, HeikoauthorFlower, Benjamin P.authorGeological Society of America and Geological Society of London, InternationalpublisherdocumentHardcopyIn: Anonymous, Earth system processes; programmes with abstracts94The late Oligocene to early Miocene (20-26 Ma) is characterized by a complex climate history that includes a stepped transition toward a cooler climate, intermittent partial glaciations of Antarctica, and a transient glaciation, Mi-1, at the Oligocene/Miocene (O/M) boundary. The Mi-1 event is characterized by an anomalous positive oxygen isotope excursion, the magnitude of which suggests the brief appearance of a full-scale ice-sheet on east Antarctica coupled with a few degrees of deep sea cooling. A recent breakthrough in extending the astronomical calibration back to approximately 30 Ma has provided a unique opportunity to compare the climatic events of the O/M transition relative to Earth's orbital variations. Here, we present an uninterrupted 5.5 My long high-fidelity chronology of late Oligocene-early Miocene climate and ocean carbon chemistry that is based on a composite isotope time series from two deep-sea cores (ODP Sites 926 and 929) collected in the western equatorial Atlantic. This unique isotope record provides a rare window into how the climate system responded to orbital forcing under boundary conditions significantly different from those of the recent past. Time-series analyses reveal climate variance concentrated at all Milankovitch frequencies, but with unusually strong power at the primary eccentricity band periods of 406, 125, and 95-ky. These cycles, which represent in part glacial advances and retreats of Antarctic ice-sheets, show significantly enhanced variability over a 1.6 My period (21.4-23.0 Ma) of suspected low greenhouse gas levels as inferred from the carbon isotope record. Perhaps the most unexpected finding is that of a rare orbital congruence between eccentricity and obliquity that precisely corresponds with the Mi-1 glaciation. This orbital anomaly involves approximately four consecutive cycles of low amplitude variance in obliquity (a node) during a period of low eccentricity. The net result is an extended period ( approximately 200 ky) of low seasonality orbits which allow for a step-like expansion of an Antarctic ice-sheet.completedStratigraphyancient ice agesAntarcticaAtlantic Oceanboundary conditionsCenozoicchronologyclimate changeclimate forcingcorescyclesEquatorial Atlanticgeochemistryglacial environmentglacial geologyglaciationice sheetsisotope ratiosisotopesLeg 154lower Miocenemarine sedimentsMilankovitch theoryMioceneNeogeneO-18/O-16Ocean Drilling ProgramODP Site 926ODP Site 929Oligoceneorbital forcingoxygenpaleo-oceanographypaleoclimatologyPaleogenesedimentsstable isotopesstatistical analysisstratigraphic boundaryTertiarytime series analysisupper OligoceneWest Atlanticurn:org.iodp:exp:154urnlargerWorkCitationcampaignurn:org.iodp:exp:154:site:926urnlargerWorkCitationstudyurn:org.iodp:exp:154urnlargerWorkCitationcampaignurn:org.iodp:exp:154:site:929urnlargerWorkCitationstudyurn:org.iodp:exp:154urnlargerWorkCitationcampaignEnglishgeoscientificInformation-43.4423-42.54303.43095.5834