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Lateral heterogeneity in paleosols and implications for proxy use

Technical talk presented at GSA Annual Meeting 2020. The geochemistry of paleosols (fossil soils) can be used to reconstruct past climates because soils form as a direct response to conditions like precipitation and temperature. Tools to reconstruct these past climates (paleoclimate proxies) typically only incorporate statistical uncertainty associated with the regression defining the proxy, rather than incorporating other types of uncertainty. Additionally, studies that use paleosols are inherently limited by the extent of the geologic outcrop (i.e., how much rock is exposed and accessible for sampling?), but little research has been done on how the geochemistry of laterally-extensive paleosols varies across kilometer scales. Here, we show that geochemistry is relatively consistent (with Ca being the main exception)–good news for proxy use–but demonstrate that the number of individual paleosol sites (profiles) sampled affects our ability to confidently make quantitative paleoclimate interpretations. We suggest sampling multiple profiles and incorporating site-specific uncertainty based on the extent/coverage and, as a rule of thumb, considering relative rather than absolute (quantitative) change in paleoclimate proxies.