WHAT COMES NEXT FOR PALEOSOL PALEOCLIMATE PROXIES?

Whereas there were once questions about whether paleosols provided useful paleoclimatic or paleoenvironmental information (or even if they existed!), the past few decades have seen a variety of innovations using elemental geochemistry and organic and inorganic isotope geochemistry to move beyond descriptive paleosol studies to quantitative ones. In addition, rudimentary sedimentologist-level understanding of soil formation in the geologic community has been replaced in many cases by a new generation of scientists with deeper, more process-based knowledge. Dr. Steven Driese spent his career as one of the key figures in both of those transitions and for that, we honor him today. His work and the work of others have set a stage for a more nuanced understanding of the paleosol record. For example, to be truly useful for future climate projections, being able to understand paleo-seasonality or paleo-growing season precipitation from paleosols is far more important than understanding the mean climate state. However, that greater nuance also demands greater rigor. For example, does the proxy have equal validity as a forward model or only as a reverse model? Can a single feature (e.g., depth to the Bk horizon, “salinization” ratio) be related to multiple environmental factors, and if so, what other information is needed to determine robustly which factor(s) is/are the driving factor? Moving forward, what features should we demand of future proxies and future refinements of existing proxies? (1) Proxy relationships should not simply be statistical, they should be based in soil science and should have a strong theoretical underpinning. (2) Data analysis should include both spatial and temporal uncertainty and not simply analytical or reverse model fit uncertainties. (3) Proxy relationships should be based on standardized analytical methods (e.g., sample treatment methods). (4) Proxy relationships should incorporate stratigraphic contingencies (e.g., the evolution of C4 plants). I will briefly discuss examples of each of these four principles by looking at where we have been and where we might go.