Abstract

Oscillations in the time series of insoluble microparticle characteristics between 0.7 and 11.0 μm in the Greenland Ice Sheet Project 2 (GISP2) ice core reflect changes in environmental conditions in the Northern Hemisphere from 10 500 to 14 000 yr ago. Elevated values in microparticle number and mass, especially during the Younger Dryas, are related to Northern Hemisphere aridity and the subsequent increase in dust available for long-range transport to Greenland. This scenario occurs with the colder climatic conditions that result from a more expanded (spatially and temporally) polar vortex. Peaks in mean grain size based on number (mean number diameter) are a proxy for increased strength in zonal winds (westerlies). Highs in mean number diameter in the earlier part of the record often coincide with number and mass peaks reflecting the increased temperature and pressure gradients with an expanded polar vortex. Highs in mean grain size based on mass (mean mass diameter) reflect greater deposition of the coarser size fraction, and thus are a proxy for increased storminess associated with better developed synoptic-scale pressure systems in the northernmost Atlantic region. Peaks in mean mass diameter often lead these other parameters by 100–200 yr, suggesting an increase in storminess with the initial southward migration of the mean position of the polar front prior to full development of a more expanded polar vortex. The general decline in number and mass trends (decreased aridity with a contracting polar vortex) together with increasing mean number diameter trends (strengthening zonal winds) following the maxima in the early Younger Dryas suggest an expansion of mid-latitude circulation systems (subtropical highs), thereby maintaining latitudinal temperature and pressure gradients. Increased variability in mean mass diameter during the warm Preboreal, compared to the colder Younger Dryas, may be a function of the greater seasonality during warmer climatic periods, and thus more frequent storms associated with higher frequency oscillations in the position of the polar front with changing seasons and increased interannual variability in climate.

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