Holocenic proxies of sedimentary organic matter and the evolution of Lake Arari-Amazon Region

Four sediment cores were sampled from Lake Arari, located on Marajó Island at the mouth of the Amazon River. The islandʹs vegetation cover is composed mainly of Amazon coastal forest, herbaceous and varzea vegetation. The integration of data on sedimentary structures, pollen, carbon and nitrogen isotope records, C/N ratios and radiocarbon ages allowed the identification of changes in vegetation and the sources of organic matter accumulated in the lake during the Holocene. The data indicate a relatively high flow energy, marine water influence and the presence of mangroves during the lagoon phase between 8990 and 8690 cal yr B.P. and 2310–2230 cal yr B.P. Between 2310 and 2230 cal yr B.P. and ~ 1000 cal yr B.P., the flow energy decreased and the mangroves were replaced by herbaceous vegetation following the decline in marine influence, likely due to the increase in freshwater river discharge. During the last 1000 years, Lake Arari was established in association with the expansion of herbaceous vegetation and the dominance of freshwater algae.