Factors controlling the geochemical composition of Limnopolar lake sediments (Byers Peninsula, South Shetland Island, Livingston Island, Antarctica) during the last ∼ 1600 years

Abstract

Abstract. We sampled a short (57 cm) sediment core in Limnopolar Lake (Byers Peninsula, Livingston Island, South Shetlands Islands), which spans the last ~ 1600 years. The core was sectioned at high resolution and analyzed for elemental and mineralogical composition, and SEM-EDS analysis of glass mineral particles in selected samples. The chemical record was characterized by a contrasted pattern of layers with high Ca, Ti, Zr, and Sr concentrations and layers with higher concentrations of K and Rb. The first also enriched in plagioclase and, occasionally, in zeolites, while the later were relatively enriched in 2:1 phyllosilicates and quartz. This was interpreted as reflecting the abundance of volcaniclastic material (Ca-rich) vs. Jurassic-Lower Cretaceous marine sediments (K-rich) – the dominant geological material in the lake catchment. SEM-EDS analysis revealed the presence of abundant volcanic shards in the Ca-rich layers, pointing to tephras most probably related to the activity of Deception Island volcano (located 30 km to the SE). The ages of the four main peaks of volcanic-rich material (AD ~ 1840–1860 for L1, AD ~ 1570–1650 for L2, AD ~ 1450–1470 for L3, and AD ~ 1300 for L4) matched reasonably well the age of tephra layers (AP1 to AP3) previously identified in lakes of Byers Peninsula. Some of the analyzed metals (Fe, Mn, Cu and Cr) showed enrichments in the most recent tephra layer (L1), suggesting relative changes in the composition of the tephras as found in previous investigations. No evidence of significant human impact on the cycles of most trace metals (Cu, Zn, Pb) was found, probably due to the remote location of Livingston Island and the modest research infrastructures – local contamination was found by other researchers in soils, waters and marine sediments on areas with large, permanent, research stations. Chromium is the only metal showing a steady enrichment in the last 200 years that could be interpreted as recent anthropogenic contamination. At the same time, some features of the chemical record suggest that climate may have also played a role in the cycling of the elements, but further research is needed to identify the underlying mechanisms.