Influence of orbital parameters on Pleistocene loess deposition in central Alaska

Abstract

Few long proxy climatic records are available from terrestrial locations. The isotope records of Pleistocene climate change found in marine cores reflect worldwide ice-volume and temperature changes forced by variations in the Earth's orbital geometry. Comparable terrestrial records are rare. Loess (wind-deposited silt) is perhaps the closest terrestrial analogue to marine sediments in that both result from more-or-less continuous deposition of fine-grained sediment. Here we examine the hypothesis that mag-netic susceptibility variations through loess sections reflect climate forcing. We statistically tested cross-correlations between high-precision, orbitally tuned marine oxygen isotope curves recording the past 250,000 yr BP, and magnetic susceptibility profiles through a thick loess section in central Alaska. Highly significant (P> 0.0001) correlations indicate strong, thick palaeosols formed in Arctic loess during early parts of interglacial periods correspond-ing to isotope stages 7 and 5. Thinner soils formed during interstadial events corresponding to early stage 7 and stage 3. Autocorrelation and time-series analysis of the loess data show spectral peaks at 125,000, 41,000 and 23,000 yr BP, showing for the first time that terrestrial orbital periodicities influenced and are recorded in proxy climatic data from terrestrial aeolian deposits at high latitudes.