Soil and Paleoclimatology.

Climate imparts an enormous imprint on soil. For decades, soil researchers have recognized that gravelly arid soils accumulate laminar growth bands of carbonate on gravel bottoms and as caps on indurated carbonate layers. Over time, theoretical and instrumentation advances have begun to make it possible to both accurately date the growth bands and derive precise isotope records that rival the precision of other more well known methods of climate reconstruction. These “pedothems” (Oerter et al. 2016. PNAS 113:919-924)– the pedogenic equivalent of spelothems – provide exciting research opportunities and questions for the foreseeable future. First, recent innovations in U series dating (laser ablation ICPMS) and stable isotope analyses (secondary ionization mass spectrometry) represent a revolution in spatial and temporal analyses of pedothems, and at the present time these tools still have not been exploited to their full potential. Second, more research on the in-soil replication of pedothem records, and variations with depth, are needed to both ascertain the reliability of the data and to glean more environmental information from a given soil. Third, in some environments it is clear that well-preserved carbonate pedothems exceed the time frame of U series dating capabilities (~ 300 – 350 ky), and that new isotope systems will need to be employed to push carbonate dating back into time. Finally, high resolution trace element chemistry – combined with isotope records – may provide substantial new information about changes in dust sources, chemical weathering, and other soil processes over time. It is now a unique time in the history of carbonate research, one where soils will provide new and unforeseen insights into the recent climate past.