The influence of biological and environmental factors on the stable isotopic composition of ostracods – the Late Pleistocene record from Lake Albano, Central Italy

Abstract

The stable oxygen and carbon isotopic composition of ostracod valves is the result of the interaction of several variables. Understanding and identifying the biological and ecological factors influencing the life of these animals improves the interpretation of isotopical data, and leads to better paleoenvironmental reconstructions. Ostracod biostratigraphy and determinations of oxygen and carbon stable isotopes on ostracod valves were carried out on a short sequence of the Last Glacial Maximum from Lake Albano (Central Italy). The oxygen isotopic composition of adults of Candona neglecta ranged between 0.5‰ and 1.5‰, and in Ilyocypris bradyi between –2‰ and –0.5‰ . Isotopic values from adults of C. neglecta fell within the range –1.5‰ to –0.8‰ when corrected for vital effect. The carbon isotopic signal ranged from 9.4‰ to 10.8‰ in adults and juveniles of C. neglecta, and from 9.8‰ to 11.3‰ in I. bradyi. Differences between left/right valve and gender were negligible, whereas there appeared to be a marked influence of life stage and species-specific factors related to vital effect and differences in microhabitat and seasonality. We combined analyses on carbon and oxygen isotopes with information deriving from ostracod ecology to reconstruct short term oscillations in past lake water level. Seasonal changes in either the temperature or the isotopic composition of the lake water were also identified. Relatively high δ18O values in ostracod valves were probably associated with the lake location and source of moisture, while high δ13C values were most probably related to the input of volcanic CO2 into the lake.