Pedogenesis and landscape evolution of Calcisols on Quaternary carbonatic sediments of Fernando de Noronha and Trindade volcanic islands, South Atlantic

Abstract

Carbonate-rich soils are found in different materials, climates, and environments, and are generally characterized by alkaline pH values and high base saturation, dominated by exchangeable Ca2+. Fernando de Noronha and Trindade volcanic islands, in South Atlantic, register carbonate-rich soils on bioclastic sediments at coastal areas. This study aims to investigate the pedogenic evolution of these soils associated with landscape processes. Six profiles were described and sampled, four of which located on bioclastic sediments (PN1, PN2, PT1, and PT2), one on Quaternary fluvial sediments (PN3), and one developed on calcarenites overlying ankaratrite flows (PN4). Morphological, physical, chemical, mineralogical, micromorphological and microchemical investigations were carried out, and principal component (PCA) and statistical analyses were applied to all data. The soils were classified as Calcisols, Fluvisol, and Cambisol and the results suggest that the carbonatic parent material and local climate are the main drivers of soil genesis, subordinated by biogenic and landform processes. All profiles have high exchangeable Ca2+, base saturation, pH, CaCO3 equivalent, and total Ca content, with calcite and aragonite minerals. Pedogenic carbonates features occur in all soil, being more developed in Fernando de Noronha Calcisols, and partially dissolved in Trindade Calcisols. The contrasting landscape and climate evolution between these islands explain these differences. Hence, these insular Calcisols are products of varying pedological evolution, with Holocene paleoclimates as the main factor of differentiation. Our results indicate the adoption of “bioclástico-carbonático” sub-group for Calcisols and Fluvisols from Fernando de Noronha, proposing the inclusion of “bioclástico-chernossólico” sub-group in the Brazilian Soil Classification System.