INTERPRETATION OF PALYNOLOGICAL DATA FROM SEDIMENT CORES COLLECTED IN POTENTIALLY “NOISY” ENVIRONMENTS

Deciphering the frequency and timing of natural or human disturbance on the landscape helps society understand and thereby mitigate risk. For example, increase in the frequency of extreme weather events over the last couple of decades has driven interest to improve the resolution of century- and millennial-scale records of past environmental change in order to predict future change, or at least to show that what's happening today is unprecedented in the geologically recent past. Sometimes lakes with beautifully annually-laminated sediment, typically high-elevation lakes near treeline, archive these changes; but in other locations and to answer different questions, the critical sedimentary archive may lie beneath wetlands and low-elevation lakes where annual resolution is not revealed in sediment stratigraphy and/or sedimentation patterns are dynamic. To illustrate some of the problems encountered when working in dynamic sedimentary environments, I will present palynological evidence for past earthquakes archived in intertidal marshes of Cascadia and Alaska-Aleutian Subduction Zones. Examples will demonstrate the importance of understanding basin bathymetry, sediment/peat stratigraphy, potential for post-deposition mixing (physical and biotic), and modern ecology. Though the intertidal marshes are dynamic, calculation of preseismic uplift and post-seismic rebound is possible using modern analogues to calibrate fossil assemblages to past sea level. Learned principles from the earthquake paleoecology examples are applied to studies of floods and anthropogenic modification of the landscape. To interpret palynological data, especially from dynamic sedimentary environments, a high-resolution, isotope-derived age-depth model sufficient to reveal variable sediment accumulation rates is paramount. An understanding of sediment geochemistry may help to identify changes in sediment source and reworked sediment. Regardless of disturbance type or quality of the sediment, combine palynology with the study of other fossils (such as plant macrofossils or diatoms) and study change with depth in the physical attributes of the sediment. A multivariate approach will reduce uncertainty or at least make the uncertainty more realistic.