The carbonate minerals that form within paleosols are thought to record the composition of soil water and gas in ways that permit the determination of ancient atmospheric CO₂. However, critical uncertainties in established soil carbonate-based proxies (e.g. ¹³C/¹²C ratios) have limited past paleoclimate reconstructions. To address this problem, this project aims to develop a new boron proxy (δ¹¹B) that will provide complementary yet orthogonal constraints on soil chemistry and atmospheric CO₂, strongly constraining ancient atmospheric compositions and ecosystem responses to carbon cycle perturbations. The key hypothesis that drives the development of this B proxy is that the pH dependence of B speciation allows for the B existing within paleosol carbonates to be used as a proxy for pore space CO₂ concentrations.

This method project will further the investigation of this hypothesis by using LA-ICP-MS analysis to create two 2D maps of soil carbonate nodules. Using iolite4 software and images of the nodules, bright and dull luminosity will be identified and the corresponding areas on the 2D element maps will have their pixels pooled to regress boron against other trace element concentrations as a function of luminosity. The objective of this project is to see whether grouping neighboring pixels of comparable luminosity can be applied to reveal trends in trace element concentrations in the bright and dull carbonate regions of the two nodules.