POTENTIAL FOR HIGH-PRECISION AGE MODELS FOR TERRESTRIAL CLIMATE ARCHIVES USING RADIOCARBON AGES OF POLLEN SEPARATED BY FLOW CYTOMETRY

Documenting the existence, magnitude and direction of leads and lags in records of global and regional climate change is critical to understanding the behavior of Earth’s climate system. In particular, Holocene climate changes have occurred under boundary conditions similar to the present (insolation, ice sheets, ocean/atmosphere circulation), and are well preserved in many terrestrial archives. However, the uncertainties in the ages of past changes from lake, wetland, and other environments are often at least 100 years, making it difficult to distinguish synchroneity and feedbacks between archives. This is often due to the lack of terrestrial macrofossils in climate-sensitive locations, such as high-alpine or dryland settings, and is also in part due to the need to calibrate radiocarbon ages to calendar years. Radiocarbon dating of pollen separates has long been attempted to improve the resolution of age models, but the difficulty of cleanly separating pollen from other kinds of organic carbon of different (or indeterminate) age has prevented its reliable use. Separation of pollen by flow cytometry holds the potential to provide high-precision and –accuracy age models, because the pollen can be separated completely and very efficiently.

Here we report radiocarbon ages on pollen from a set of closely spaced samples from the Holocene sediments of Mono Lake, California, using flow cytometry to achieve pure separates. The accuracy of the pollen ages is tested using two well-dated tephras, the South Mono tephra (1300-1355 cal yr BP; Bursik & Sieh, 2013; USGS Data Series 758) and the North Mono-Inyo tephra (600 yr BP; Millar et al. 2006; QR v66 p273), that bracket the samples. This time period encompasses two regressive-transgressive cycles at Mono Lake, and includes the severe drought of the Medieval Climate Anomaly. The samples are spaced 1-2 cm apart, providing the opportunity to test superposition and increase the precision of the age model by matching the ¹⁴C ages to features of the IntCal13 calibration curve. If this approach works it will provide the potential for decadal-scale precision on the ages of paleoclimatic features.