Your query was: medeiros

HR: 0830h
AN: OS51B-26
TI: The Global Ice Volume Record as Viewed Through a Benthic \delta$^{18}$O Stack
AU: Medeiros, B P
EM: brianpm@uclink4.berkeley.edu
AF: Department of Physics, Univeristy of California, Berkeley, CA 94720 United States
AU: * Karner, D B
EM: dkarner@socrates.berkeley.edu
AF: Department of Physics, Univeristy of California, Berkeley, CA 94720 United States
AU: Muller, R A
EM: ramuller@lbl.gov
AF: Department of Physics, Univeristy of California, Berkeley, CA 94720 United States
AU: Levine, J
EM: jlevine@socrates.berkeley.edu
AF: Department of Physics, Univeristy of California, Berkeley, CA 94720 United States
AB: Stacked marine isotopic records, such as the Specmap and Low Latitude stacks, were constructed in the past in order to gain a clearer picture of global climate change. In the stacking of multiple records, local climate variations in any one core are reduced by their absence in the other cores, allowing global variations to dominate the composite record. These two stacks have been used to address a number of scientific questions involving the effects of Earth's orbital variations on climate. But there are limits to their applicability to the study of global ice volume. The Specmap stack is composed of five planktonic \delta$^{18}$O records. Two of these records do not reach marine isotopic stage 9, and thus contribute little to our understanding of the $\sim$100 kyr glacial cycle that has dominated the global ice volume signal over the last million years. The Low Latitude Stack is composed of only two planktonic \delta$^{18}$O records, and therefore is unlikely to have local climate effects averaged out, if only because of the small number of cores used. We argue that these stacks are not optimum for studying global ice volume history, since planktonic \delta$^{18}$O records reflect, in part, surface water effects that are unrelated to global ice volume. To study global ice volume, we have constructed a stacked record using benthic \delta$^{18}$O data, which we believe is a better proxy for global ice volume than are the planktonic stacks. Our stacked record was constructed from five cores, using an automated procedure that enables us, at each step, to minimize personal bias. The criteria used to construct the stack are as follows. We set the preliminary time scale for each core using radioisotopically based tie points at Termination II = 135 $\pm$ 5 ka, Termination V = 434 $\pm$ 13 ka, and the Brunhes-Matuyama geomagnetic reversal = 790 $\pm$ 20 ka. The top of the core was pinned to an age of 0 ka. We assume a constant sedimentation rate between these tie points. We then apply a band-pass filter to isolate the obliquity component in each record (obliquity is the only universally accepted orbital signal in the global ice volume record). The maxima of the band pass filtered data are then aligned with obliquity maxima, and later one overall phase shift per core is permitted to restore the age of the core top to 0 ka. The resultant obliquity-tuned sedimentation rate is then used to stack the cores' unfiltered data. Only cores that could be treated by the automated program in an internally self-consistent way are used in the stack, and no cores that met these criteria were excluded. The benthic stack makes a definite quantitative prediction of global ice volume and sea level through time, with estimated uncertainty. This prediction may be tested by comparison with sea level estimates derived from marine terrace studies. This sea level history should be useful in addressing the uplift rates of tectonically active coastal margins, and in outstanding issues of astronomical forcing of climate change.
UR: http://muller.lbl.gov
DE: 4267 Paleoceanography
DE: 4804 Benthic processes/benthos
DE: 3099 General or miscellaneous
DE: 1635 Oceans (4203)
SC: OS
JN: Eos Trans. AGU, 81 (48), Fall Meet. Suppl., 2000
MN: Fall Meeting 2000