On the Sadler Effect and biases in Holocene paleofire records

Abstract

Relationships between rates of change in Earth-surface systems and their measurement durations suggest that rates may be critically dependent on durations of observation. Studies relating rates and durations of change have appeared increasingly over the past 50 years, with many specifically discussing the importance of the ‘Sadler Effect’, the observation that plots of log duration versus log rate commonly define trends with slopes approaching minus unity toward shorter durations. Concurrently, paleofire research focusing on sedimentary charcoal in lakes has exhibited a similar profusion, with recent paleofire studies noting that both sedimentation rates as well as charcoal accumulation rates share a negative power law relationship with the time span of their measurement, suggesting longer time spans may be inherently biased toward lower charcoal fluxes because of the greater incorporation of sedimentary hiatuses over longer time intervals of measurement.Here we examine the premise that paleofire lake records might exhibit systematic biases because of the greater temporal completeness of younger successions. We evaluate the importance of preservation biases through examination of Holocene increases of sediment deposition and charcoal accumulation rates in 14 Alaskan lakes, and conclude that observed negative trends apparent in log duration versus log rate plots are a result of time as a variable in both axes (duration and rate). However, such self-correlation does not preclude the possibility of a systematic incorporation of sedimentary hiatuses in older portions of these sedimentary records. Age-dating and modelling techniques employed in paleofire research do not allow us to decide if these patterns stem from purely ‘Sadlerian’ preservation bias. Regardless, dependencies of process rate on process duration in these, as well as other, sedimentary archives have the potential to impact paleofire interpretations. Disentangling the drivers and biases inherent to paleofire archives is especially important due to climate change and the increasing need to establish paleofire baselines.