THE IMPLICATIONS OF ATMOSPHERIC POLLEN RAIN FOR FOSSIL POLLEN PROFILES IN THE ARID SOUTHWEST (AEROBIOLOGY, PALAEOBOTANY, TAPHONOMY, PRESERVATION).

Abstract

I compared atmospheric and soil pollen values to determine taphonomic influences on pollen in Southwestern soils. Burkard traps sampled atmospheric pollen for six years from multiple sites in Tucson, Arizona. Tauber and soil samples were collected for two years at Tumamoc Hill (Tucson). Morus, Ambrosia, Gramineae, and Chenopodiaceae-Amaranthus characterize Tucson's airborne pollen. Artemisia, Garrya and summer Pinus pollen are transported from the mountains. Annual pollen capture is similar between Burkard and Tauber samplers. Atmospheric pollen is seasonally variable; annual variability is low. Spatial variability among sites is low. Pollen concentrations vary widely among sites, but taxonomic composition remains constant. Reentrained soil pollen comprises 11% of the airborne pollen. Gramineae and Chenopodiaceae-Amaranthus pollen comprise 90% of the reentrained pollen. Pollen reentrainment varies seasonally. High maximum and minimum temperatures, low dew point and moderate wind speeds are associated with maximum atmospheric pollen concentrations. Winds preceding summer storms cause increased pollen concentrations. Deterioration characterizes pollen from soils. Chenopodiaceae-Amaranthus, Ambrosia, Other Compositae and Graminear are commonly found; Morus is rarely found. Pinus, Sphaeralcea, Boerhaavia and Kallstroemia are present in low numbers. These taxa have thick pollen walls, and they resist destruction. Seasonally collected soil samples have similar pollen spectra. Seasonal airborne pollen variability does not affect the soil pollen spectra. Inoculated soil pollen is well preserved, but pollen is lost rapidly. After one year, pollen concentrations approached background levels for seven of the eight pollen taxa tested. Solidago remained an order of magnitude higher. Pollen morphology may play a role in differential pollen loss. Pollen from the inoculated plots is lost through post-mortem transport. Pollen in soils is time-averaged and exhibits little temporal variability. The average airborne pollen spectra differs from the pollen in the soil. Soil pollen was degraded; inoculated plot pollen was well preserved. I conclude airborne pollen contributes little to the soil pollen of Tumamoc Hill. The soil pollen spectra is affected by selective- or non-deposition of airborne pollen (e.g. Morus), differential pollen destruction, and differential post mortem transport.