Effects of island weathering and natural iron fertilization in the geochemistry of deglacial sediments from the Kerguelen Plateau, Southern Ocean

Abstract

Elemental abundances and their associations in marine sediments near the Kerguelen Plateau can reveal the influence of island weathering on regional biogeochemistry, including natural iron fertilization. In this study, we evaluate the effects of oceanic processes in sediment column geochemistry at the northern flank of the Kerguelen Plateau using a 1.04 m long core (SOE11-01) collected during the 11th Indian Southern Ocean expedition. The AMS radiocarbon dates show that the sediment belongs to the deglacial period. The deep-reaching and fast-flowing Antarctic Circumpolar Current (ACC) driven strong current activity resulted in sediment redistribution. Major elements include Al, K, Mg, Ca, Fe, Ti and Mn with an average concentration of 4.01%, 1.30%, 1.32%, 11.39%, 3.81%, 1.12% and 0.05%, respectively. While the minor elements are Co, Cu, Zn, Ni, V, Sr, Ba, Cr and Pb, with an average of 28 ppm, 29 ppm, 103 ppm, 24 ppm, 109 ppm, 324 ppm, 343 ppm, 52 ppm, and 54 ppm, respectively. We did the regression and factor analysis of the geochemical dataset. The first factor represents 53% of the total variance and is loaded with elements Al, K, Fe, Mn, Ti, Cr, Co, Zn, Pb, and V. The strong associations of these elements imply their terrigenous origin mainly from the Kerguelen Plateau, which is the nearest land mass. The strong association of Mn with Fe and Co suggests the oxic depositional environment due to the oxygenated ACC waters. Fe and productivity indicators, i.e., Fe/Al and Ba/Al, are strongly correlated due to the prevalence of natural iron fertilization during deglaciation. Despite the island-driven regenerated and weathered Fe-induced productivity, Fe and Corg are negatively correlated due to the lack of preservation of Corg in the oxic waters. The geochemical characteristics of the parent rocks get altered by the regional biogeochemistry, especially by natural iron fertilization.