Sediment composition and its effect on the productivity in Larsemann Hills, East Antarctica

Abstract

The sediment cores collected from lakes L-8, L-10, and L-12 of Larsemann Hills, East Antarctica, were investigated for sediment components (sand, silt, clay, total organic carbon, total nitrogen, total phosphorus, elemental TOC/TN ratio, and biogenic silica or biogenic opal), major elements (Al, Fe, Mn, Ti, Mg, Ca), and trace metals (Cr, Co, Zn, Cd, Pb, Ba, Cu, Ni) to understand the source, processes, and productivity in the lacustrine sediments. In lake L-10, average sand content was higher than in lakes L-8 and L-12 which indicated the high intensity of mechanical weathering, resulted in releasing coarse-grained material from the rocks in the catchment area. High Ti/Al molar ratios (2.00–3.32) in all the three cores resulted from shorter transportation distance from different parent sources. Higher clay content near the surface in all the three lakes indicated deposition of fine-grained particles supplied by ice-melt water owing to ice-free conditions in the area in recent years. Relatively, higher biogenic silica along with high total organic carbon associated with high clay in the upper section of lakes L-10 and L-12 and middle section of core L-8 indicated deposition of finer particles from suspension which facilitated high primary productivity due to exposure of the lakes to the ice-melt water influx. Further, Mg/Ca ratio in all the three lakes was high near the surface indicating enrichment of biogenic sedimentation. C/N ratio was found to be much less than 10, indicating the major source of organic matter is autochthonous and exclusively derived from algae (C/N < 10) in all the cores. The metal concentration was found to be higher in core L-8 and was found to be associated with finer sediments, as compared to cores L-10 and L-12 where coarser sediments must have diluted the metal content. Ba was found to be of biogenic origin in cores L-8 and L-12 while in core L-10 it was of lithogenic origin. Cd, Zn, and Ni in all the three lakes were found to be mainly of biogenic origin, whereas all other metals studied were of lithogenic origin. Thus, the concentration of trace metals in Larsemann Hill lake sediments is entirely by natural processes regulated by lithology, catchment processes, and climatic conditions.