Dust Deposition in Ice Cores and Ocean Sediments as a Constraint Upon the Magnitude of the LGM Dust Cycle

While the functional dependence of dust emission upon wind speed is known from observations, the absolute emitted mass must be constrained indirectly, often using retrievals of dust aerosol optical thickness. Currently, total dust emission (and the total aerosol mass of dust) for the Last Glacial Maximum (LGM) is calculated in the NASA GISS Earth System ModelE using measurements from the present day (PD). Model emission and aerosol load are constrained in a simulation of the PD, and the LGM dust cycle is calculated after introduction of LGM dust source and vegetation data sets. Thus, the LGM dust cycle is subject to model errors in the PD simulation. Here, we constrain the LGM dust cycle directly, using deposition measurements from ice cores and ocean sediments. This gives an independent estimate of the total dust load in the LGM as well as the PD load after the LGM dust source and vegetation file are replaced with their PD counterparts. Consistency of the two LGM dust estimates (constrained either by LGM or PD measurements) is a measure of uncertainty. We also consider which deposition measurements and locations provide the strongest constraint on the LGM dust load.