A 6000 yr record of climatic variability for the Usumucinta-Grijalva delta, Mexico, based on a palaeoecological transect

Within the floodbasin of the Usumacinta-Grijalva delta in Tabasco, southern Mexico a continuous accumulation of organic deposits occurred since 6000 years ago. Suitable locations allow a detailed reconstruction of environmental changes modulated by human impact, sea-level, and climate change since the dawn of Olmec and Maya cultures. Five sediment cores along a 10 km transect were studied on pollen and macro-remains. The transect runs from drowned ancient beach ridges with evidence of human occupation towards a relatively undisturbed partly infilled lagoon. Multiple tephra layers within the organic sediments were used for correlation between cores, supported by 25 AMS radiocarbon dates on terrestrial macro-remains yielding a solid stratigraphic framework for the reconstructed environmental changes. The study of multiple cores along a transect allowed for the exclusion of local influences on the pollen signal and enabled us to unravel the impact of sea-level rise, human land use and climate change. Vegetation changes reveal the transition from an optimal climatic period towards a strong climatic variability during the Late Holocene. The advance and retreat of coastal ecosystems appears to be strongly determined by the duration of the hydroperiod which we relate to changes in river discharges and rainfall in the drainage basin. Our results can be compared to other late Holocene climatic proxy records from southern Mexico.