The transition from the mid-to late-Holocene in MesoAmerica saw increasing complexity in spatial patterns of change. Records from the western part of the region are sparse, with lacustrine sequences affected by long term anthropogenic disturbance or lacking chronological resolution. Here, we present a continuous palaeoecological and geochemical record from Laguna de Juanacatlán, a remote lake in the mountains of the western TMVB. Diatom assemblages, XRF scanning data and bulk organic geochemistry from a well-dated, 7.25-m laminated sequence were combined with summary pollen data from a 9-m partially laminated core to provide a continuous record of catchment and lake ecosystem changes over the last c. 6000 years. Relatively humid conditions prevailed prior to c. 5.1 cal ka, which supported dense oak-pine forest cover around a deep, stratified lake. A trend towards drier conditions began c. 5.1 cal ka, intensifying after 4.0 cal ka, consistent with weakening of the North American Monsoon. Between 3.0 and 1.2 cal ka, lower lake levels and variable catchment run-off are consistent with increasing ENSO influence observed in the Late Holocene in the neotropics. From 1.2 to 0.9 cal ka, a marked change to catchment stability and more intense stratification reflected drier conditions and/or reduced rainfall variability and possibly warmer temperatures. After 0.9 cal ka, conditions were wetter, with an increase in catchment disturbance associated with the combined effects of climate and human activity. In recent decades, the lake ecosystem has changed markedly, possibly in response to recent climate change as well as local catchment dynamics.
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We thank colleagues from the Lacustrine Core Repository, University of Minnesota, the Universidad Nacional Autónoma de México and the Universidad Michoacana de San Nicolás de Hidalgo, who were involved in coring as part of the MesOamerican Lakes Expedition (MOLE). Fieldwork in 2003 was supported by The Aberystwyth University , the University of Nottingham , UNAM and UMSNH . Radiocarbon dating was provided through UK NERC ( 1108.0305 ) and organic geochemical analyses through the UK NERC Isotope Geosciences Facilities ( IP/827/1104 and IP/853/0505 ). BJA acknowledges receipt of a PhD studentship from the University of Wales, Aberystwyth. MC is supported by the USGS Climate and Land Use Research & Development Program . Antony Smith produced several of the figures. We appreciate constructive comments on the draft manuscript from David Wahl.
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