Pollen determination from sediment core of Lake Alchichica in Mexico

The pollen samples were collected from a 57-cm-long sediment core retrieved from Lake Alchichica (19° 24' 38 N, 97° 24' 14 W, 2322 masl) at a water depth of ~ 60 m using a Uwitec® coring device equipped with a 9-cm coring tube. A total of 39 wet sediment samples (1 cm³ each) were processed for pollen analysis at the Department of Geology, University of Liège, following standard acid digestion procedures. These included treatments with 10% HCl, 37% HF, acetolysis, and sieving through a 10 µm mesh. Pollen counts were performed at 400× magnification using a Zeiss microscope, with a minimum of 300 terrestrial pollen grains counted per sample.