This project will investigate physical mechanisms responsible for the 41,000-year (41-Ka) cycle in late Pliocene and early Pleistocene climate records. Previously, the researchers showed that the observed 41-Ka cycle in ice volume was forced by the equator to pole gradient in solar insolation, which controlled the meridional atmospheric heat and moisture fluxes which ultimately influenced the growth and decay of ice sheets. However, when investigating this hypothesis further using a simple coupled climate-ice model, they found that the model still fails to produce reasonable amplitude 41-Ka oscillations, and exhibits far more precessional power than do benthic foraminifera oxygen isotope signals or ice rafted debris (IRD) records (presumably due to the strong influence of summer insolation on ablation). When these data were combined with other data from other areas of the world, the analysis prompted the researchers to consider the following science questions.
* Why is modeled Northern hemisphere ice volume so small when glacial tillite deposits show ice reaching as far south as 35 degrees North latitude? Do we have problems with the models or with the interpretation of the data? * If there was a large (aerially-expansive), low elevation ice sheet on North America, ice sheet-climate models suggest it would have a large ablation zone. Why then do we not see a stronger precession signal in benthic foraminfera oxygen isotope records as ice sheet models suggest? * Could it be that the 41-Ka oscillations are due to a mechanism internal to the climate system, rather than exist only due to Milankovitch forcing?
To determine whether there is a precessional component to ice sheet variation on North America, the researchers will generate a benthic isotope stratigraphy for site 625 (Gulf of Mexico) which records meltwater pulses in planktonic foraminfera oxygen isotope records to provide a constraint on the frequency history of North American glaciation in the late Pliocene and early Pleistocene and, by extension, a constraint for ice sheet modeling.
The researchers aim to develop a new coupled climate-ice sheet model and use it to investigate different scenarios for the 41-Ka oscillations, and use the model results to reanalyze the proxy records with the objective to determine if the 41-Ka oscillations exist due to Milankovitch forcing, or are internal (self-sustained) oscillations only influenced (phase locked) by Milankovitch forcing. The researchers also will investigate the possible contribution by the Antarctic ice sheet to changes in global ice volume in the late Pliocene and early Pleistocene.
This project involves highly interdisciplinary research and enlists the fields of paleoclimate, atmospheric dynamics, physical oceanography, and climate modeling in pursuing a fundamental line of inquiry in natural climate variability. The project will support a graduate student and post-doctoral scholars working collaboratively across disciplinary boundaries and with colleagues in Norway, thus fostering a scientific collaboration between research communities in the U.S. and Norway.
