Quantifying Impedance in Pleistocene Glacial Structures
The Mid Pleistocene Transition (MPT), during which the timescales of glacial cycles shifted from ∼40 kyr to ∼100 kyr, is a widely researched yet continually unsolved issue for scientists of Earth’s paleoclimate. Obliquity, an orbital parameter which contributes to the pacing of glacial cycles, triggered a full system melt with every cycle during the early Pleistocene. However, as the MPT progressed, the trigger of full system melts began to skip obliquity cycles, contributing to the longer timescale of the late Pleistocene. A hypothesized cause of this behavior is the impedance phenomenon, where there was an increase in the climate system’s internal resiliency to changes in obliquity.
This paper seeks to quantify impedance in the PP04 conceptual climate model, as presented in Paillard & Parrenin (2004). Three geometric measures are given, which explore the internal impedance of the model and can represent the impedance evident in model runs perturbed by any random forcing term. Two measures are given which look at the response of the PP04 model to realistic forcing. Currently, impedance is only loosely defined, opening avenues for future study in further developing the definition or quantification measures of impedance. Impedance measures could, with further development, be useful as a tool for model validation.