Soil in Hawaii has been extensively studied to better understand the properties that make it effective in capturing and storing organic carbon for long periods of time. In particular, the age and rainfall gradients found naturally occurring on the Hawaiian Islands make it salient for soil research, thus far yielding insights into how mineral composition, age, and vegetation influence the abundance of soil carbon. However, the character of organic carbon along these gradients has remained virtually unknown, holding space for this study to explore how the soil profile changes with respect to the functional groups present in organic carbon molecules. This study focuses first on how previously identified properties of soil important for carbon sequestration (i.e. mineral content) independently influence sorption and collection of organic matter, and then explore how organic carbon molecule change by experimenting on whole soil samples, via experimentation on both the solid and mobile phases of the molecules. In doing so, this determination of the type of carbon present in soil and how it changes as a function of age and climate will further the understanding of soil carbon dynamics in carbon turnover and sequestration.

Carbonate rocks record information about the environmental conditions under which they formed, offering a window into Earth history. Among carbonate rocks, dolomite, CaMg(CO$3$)$2$, is abundant in the geologic record while elusive in modern environments due to kinetic barriers in formation. Geochemical signals measured in dolomite, however, are frequently used as evidence of changes to the global carbon cycle. To refine interpretations of ancient dolomite, this thesis investigates dolomite precipitation in the Coorong region of southern Australia, examining how dolomite geochemistry encodes environmental information. To that end, I create mineralogical and geochemical fingerprints of 49 samples collected from the carbonate-precipitating lakes. I develop a method for quantifying the relative abundances of carbonates from XRD spectra. I also measure carbon and oxygen isotope ratios and elemental composition (Mg, Ca, Sr, U), and, on a subset of samples, clumped carbonate isotopes to constrain formation temperatures. I use these fingerprints to evaluate whether dolomite precipitates record signals from a global carbon reservoir or are instead influenced by non-global controls like carbonate mixing processes and local environmental conditions on geochemistry. I identify two groups of isotopically and elementally distinct dolomite precipitates—one in equilibrium with atmospheric CO$2$, and one that is not. Finally, I use the fingerprints to test hypotheses about dolomite formation and show that varying levels of seawater-groundwater mixing can explain the observed chemical differences in dolomite precipitates.