Peat bog as geochemical archives of atmospheric dust deposition in eastern Canada: a multi-proxy approach

English Abstract:

Atmospheric mineral dust plays an important role in the Earth’s climate through parameters such as atmospheric radiation, cloud properties and biogeochemical cycles. While variations in dust deposition during the Holocene are not of the same magnitude as those occurring on a glacial-interglacial scale, the complex spatial and temporal variability in climate during this period was important enough to affect dust production and transport. Ombrotrophic peatlands (bogs) have proven to be valuable archives of atmospheric dust deposition as their accumulation rate over the Holocene are rarely matched by other archives.

Two peat bogs, located on the North Shore region, eastern Canada, were sampled to investigate dust deposition/palaeowinds in north eastern North America over the mid and late Holocene. Here we present geochemical (major and trace elements, Pb and Nd isotopes) records combined with ash content, particle size, plant macrofossils and bulk density for both cores. The distribution of lithogenic element (REE, Ti, Sc) concentrations within the cores show periods of increased dust deposition at Baie and IDH. The range of dust deposition varies from 0.5 to 4 g m^-2 yr^-1 in the Baie bog and from 0.1 to 2.7 g m^-2 yr^-1 in the IDH bog respectively. The higher dust fluxes in the Baie bog were recorded from 100-600 and 1000-1500 cal yr BP, originating either from greater wind intensity or drier climatic conditions. The most significant episode of dust deposition at IDH occur around 3.8 yr cal BP with a maximum of 2.1 g m^-2 yr^-1. Both cores record higher dust fluxes during the last century which suggests an anthropogenic impact on the dust cycle in the region. Before the 19^th century (1850AD), the stable Pb isotopes ratios (²⁰⁶Pb/²⁰⁷Pb) in the Baie bog range between 1.188 and 1.215, which corresponds to the value of the Canadian Shield. Neodymium isotopes analyses (on going) will allow to identify potential change in dust source which might not be recorded by stable Pb isotopes.