Using Thecamoebians to Reconstruct 1300 Years of Limnological Change at Crystal Lake, Southern California

Abstract:

Thecamoebians are microscopic unicellar organisms that live in freshwater lakes and produce tests—or shells—that are morphologically distinct to each species. The population distribution of thecamoebian species within a lake can reveal such lake dynamics as trophic status, temperature, and acidity. Crystal Lake is a small alpine lake located in the San Gabriel Mountains of the coastal southwest United States. This project’s objective is to reconstruct a 1300 yr paleolimnological record for Crystal Lake using thecamoebian assemblages. The latter reconstruction will be examined in the context of paleoclimatological interpretations from the same core (Palermo et al., 2015) to determine to what extent – if any – changes in thecamoebian assemblages respond to, and record, paleoclimatological changes such as the Medieval Climate Anomaly and the Little Ice Age. Core CLPC14-1 was extracted from Crystal Lake’s depocenter in May 2014. Grain size, magnetic susceptibility, and LOI 550°C and 950°C were measured at 1 cm contiguous intervals; additionally, C:N ratios and C and N isotopic analyses were measured every 2 cm (Palermo, 2015). Thecamoebian assemblages were analyzed in five modern surface samples, as well as throughout the core at 2 cm intervals (aligning with the other analyses performed). Statistical analysis was performed to determine significant patterns within the assemblages. Eleven AMS ¹⁴C dates of discrete organic matter (i.e. wood or charcoal) were used to generate an age model using Beacon v2.2; for the past 200 years, age control is based on correlation to Rothenberg et al. (2010) core ages (Palermo, 2015).