干旱区生态环境知识资源中心

Carbon isotopes (delta C-13(org)) in biomass, carbon (delta C-13(carb)) and oxygen (delta O-18(carb)) isotopes in authigenic calcite and estimations of chemical weathering of siliciclastic minerals (chemical index of alteration [CIA] and plagioclase index of alteration [PIA]) in lacustrine sediments of the ephemeral Babicora Basin, located within the core region of the North American Monsoon at northwest Mexico, helped to evaluate the source of biomass, variations in hydrological balance and sediment-water interactions during three different marine isotope stages (late MIS 4: >= 65.4-59.5 cal ka BP, MIS 3: similar to 59.5-28 cal ka BP and MIS 2: similar to 28-15 cal ka BP) of the last glacial. Comparisons of delta C-13(org) with previously published records of C/N, diatom abundance and fossil pollen indicate that biomass of the late MIS 4 was sourced from C-3 aquatic and land plants. During the MIS 3, the C-3 plants continued to contribute biomass and the influence of lacustrine algae, however, increased during its later part. The water column experienced more evaporation compared to two other MIS stages and sediment-water interactions varied between minimal to moderate (CIA: 49-68). Sediments were transported for longer distances during the wetter intervals and eroded from nearby lithologies during the drier intervals. Interactions between sediments and inflowing water (CIA: 59-65) remained homogeneous during the MIS 2. Source of the biomass, however, was variable. Lacustrine algae and C-3 land plants contributed biomass during the early MIS 2 (similar to 28-19 cal ka BP) and contributions from the C-4 and CAM vegetation slightly increased towards the deglaciation (similar to 19-15 cal ka BP).