Nd isotope evidence for dust accretion to a soil chronosequence in Hainan Island

Abstract: Hainan soils contain a mixture of material derived from in situ weathering of parent material plus atmospheric inputs dominated by continental dust. We use Nd isotope geochemistry to evaluate the impact of continental dust on a chronosequence of Hainan soils. The results demonstrate that dust has a profound effect on soils in 180ka and older in tropical Hainan Island. Dust is the dominant source of Nd in the oldest, most intensely weathered soils, with radiogenic dust-derived isotopic signatures (εNd(0)=−6.46) and significant high mass fraction of dust-derived Nd (75%). The fdust Nd values for soils show an increasing trend with time, implying that dust accumulates with the ages of soils. We also calculate a long term average dust accretion rates of 14.90 and 12.39mgcm−2 ka−1 at the 180 and 300ka sites; whereas the rates of the old sites are low, indicating underestimates of time-averaged dust deposition rates over million year time scales. On the basis of the geomorphic stability sites, we think that the decrease of dust inputs due to climate changes and the loss of dust due to weathering are the dominant loss mechanisms for dust and lead to underestimates of time-averaged dust deposition rates in the old sites. The results also underscore the potential for neodymium isotopes to constrain the origin of soils and paleosols. [Copyright &y& Elsevier]