Abstract

Organic matter preserved in sediments originates from aquatic and terrestrial sources in a basin. In the absence of anthropogenic influence, variation in its composition may be related to changes in climate and vegetation composition. Here, a 400 yr sedimentary record from the Barigui river was investigated using n-alkane distributions and glycerol dialkyl glycerol tetraether (GDGT) indices to assess any environmental changes which occurred in the transition from the Little Ice Age to modern times. Three stages were observed: (i) between 1600 and 1730 AD, the climate was warmer and was less humid, and herbaceous plants overlapped with woody plants; (ii) between 1730 and 1800, the temperature gradually decreased and the level of precipitation remained low, hence, so woody plants predominated; (iii) the last stage was from 1800 to the present day, when the temperature and precipitation increased, resulting in optimum conditions for the blooming of phytoplankton and aquatic plants.

Keywords: Climatic changes; Little ice age; n-Alkane distributions; GDGT proxies