Reconstruction of vegetation and low latitude ocean-atmosphere dynamics of the past 130 kyr, based on South American montane pollen types

Abstract

Strong floristic affinities indicate past ecosystem rearrangements that integrated northeast Brazil with the distant montane range of the Brazilian highlands, sustaining past plant migrations possibly due to climatic patterns. This palynological study of the marine core GL-1248 (0°55.2′S, 43°24.1′W) spans the past ~130-k years to reconstruct the montane rainforest dynamics with the predominant provenance of Parnaíba Hydrographic Basin in northeastern Brazil. In this context, the reduced continental temperatures of the last glacial enabled the migration of ontane rainforest taxa into lowland areas. In these circumstances, the pollen cluster of montane rainforest taxa increased in relative abundance during the early Marine Isotopic Stage 3. The evidence suggests that a secondary pathway evolved, instead of the widely debated coastal route, enabling the biological exchange via the expansion of montane forests throughout the central Brazilian highlands. Two montane pollen types with distinct provenance and ecological features highlighted the ocean-atmosphere dynamics. First, the increase in the relative abundance of Podocarpus correlated with periods of low moisture levels and reduced weathering in the Parnaiba Basin and led to questioning the influence of southeast trade winds as one of the leading carriers of this pollen type. Second, the evidence of Alnus pollen grains, characteristic of Andean vegetation, and low-temperature regions suggest that the Amazon river plume reached the study area. In this sense, the northeast trade winds restrained the North Brazilian Current and guided the southeastward transport of the Amazon river sediments. The presence of Alnus pollen grains emphasizes periods of a weakened North Brazilian Current. Our findings have significant climatic repercussions since heat transport to the northern hemisphere was possibly impaired at the time when Alnus occurred at our core site. • The downslope trend of the montane vegetation cluster during the last glacial period. • The ecological features and dispersal trend of Podocarpus pollen type in northeastern Brazil. • The occurrence of Alnus pollen on the western equatorial Atlantic over the last 130 kyr.