HR: 16:30h
AN: PP32D-03    [PDF]
TI: Estimates of Oligocene Sea-Level Amplitudes and Ice-Volume Changes at Milankovitch Time Scales
AU: * Pekar, S F
EM: pekar@ldeo.columbia.edu
AF: Queens College, School of Earth and Environmental Sciences, CUNY, 65-30 Kissena Blvd., Flushing, NY 11367 United States
AU: * Pekar, S F
EM: pekar@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, Route 9W, Palisades, NY 10964 United States
AU: Christie-Blick, N
EM: ncb@ldeo.columbia.edu
AF: Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, Route 9W, Palisades, NY 10964 United States
AB: Sea-level amplitudes and ice-volume changes were determined for the Oligocene at the obliquity and eccentricity time scales (41 and $\sim$ 400 ky) using high-resolution deep-sea oxygen isotope records and sea level to oxygen isotope calibrations established for Southern Ocean ODP Site 689, South Atlantic DSDP Site 522 and western tropical Atlantic ODP Site 929. Amplitudes of apparent sea-level (ASL, defined as eustasy plus the effects of water loading on the crust) for the upper Oligocene at the $\sim$ 400 ky time scale range between 25 and 30 m, and at the obliquity time scale, between 10 and 20 m. High frequency ASL changes for the lower and "mid"-Oligocene are less certain because the resolution of the records from Sites 522 and 689 is lower. At the 400 ky time scale, available evidence at these sites suggests that ASL varied by as much as $\sim$ 35 m. At the obliquity time scale, sufficient resolution is available only at Site 522, where ASL changes are estimated as between 15 and 20 m. Estimates of equivalent ice-volume changes in Antarctica at the million-year time scale suggest expansion to near the present-day volumes, collapsing in some cases to less than 15% of today's value. At the 400 ky time scale, ice volume varied by up to $\sim$ 50% of the present-day figure. At the obliquity time scale, it ranged from $\sim$ 25 to 35% of the contemporary volume. These estimates of ice volume and ASL changes were obtained by applying previously developed oxygen isotope to sea-level calibrations (Pekar et al., 2002) to the isotopic records. Correlation is good to excellent (r$^{2}$ = 0.726-0.960), suggesting that although benthic foraminiferal records are known to include a bottom-water temperature signal, temperature changes generally vary linearly with changes in ice volume. A minimum calibration for the Oligocene of 0.13% per 10 m ASL change (r$^{2}$ = 0.726) was determined from Site 689. This calibration may contain a small temperature signal, which would result in a calibration of 0.10 \permil per 10 m ASL change. An oxygen isotope to ASL calibration of 0.32\permil per 10 m ASL was determined for oxygen isotope event Mi1 (23.8 Ma) at Site 929. A calibration of 0.22\permil per 10 m ASL (r$^{2}$ = 0.960) was obtained for the lower Oligocene at Site 522, spanning oxygen isotope events Oi1 (33.5 Ma), Oi1a (32.8 Ma), and Oi1b (31.7 Ma).
DE: 4267 Paleoceanography
DE: 4556 Sea level variations
DE: 4870 Stable isotopes
DE: 9310 Antarctica
DE: 9604 Cenozoic
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting