Seasonal Bias in Soil Carbonate Formation and Its Implications for Interpreting High‐Resolution Paleoarchives: Evidence From Southern Utah

Abstract

Pedogenic carbonate is commonly used as a paleoarchive, but its interpretation is limited by our understanding of its formation conditions. We investigated laminated soil carbonate rinds as a high‐resolution paleoarchive in Torrey, Utah, USA, by characterizing and modeling their formation conditions. We compared late Holocene (<5 ka) soil carbonate conventional (C and O) and “clumped” isotopes to modern soil environment and isotope measurements: soil CO2 partial pressure, soil temperature, soil moisture, δ13C‐soil CO2, δ18O precipitation, and δ18O‐soil water. Data unambiguously identified a strong summer seasonality bias, but modeling suggested soil carbonate formed several times throughout the year during infiltration events causing dissolution‐formation reactions. This apparent discrepancy resulted from preferential preservation of calcite formed from the largest annual infiltration events (summer) overprinting previously formed calcite. Soil carbonate therefore formed predominantly due to changes in soil water content. As soil CO2 was at its annual maximum during soil carbonate formation, assuming uniformly low soil CO2 formation conditions for soil carbonate in estimating paleoatmospheric CO2 is likely not viable. Additionally, we showed modern summer δ13C‐soil CO2 and soil CO2 measurements could not produce a modeled δ13C‐soil carbonate consistent with late Holocene observations. We suggest using multiple lines of evidence to identify nonanalogous modern conditions. Finally, a nearly linear radiocarbon age model from a laminated rind showed that rinds can be used as a high‐resolution paleoarchive if samples are from a single depth and the timing and conditions of soil carbonate formation can be constrained through time.

The δ13C, δ18O and Δ47records in biogenic, pedogenic and geogenic carbonate types from paleosol-loess sequence and their paleoenvironmental meaning

“…In contrast, some pedogenic carbonates (e.g., rhizoliths) may form over a few decades (Gocke et al, 2011). Pedogenic carbonate nodule and pendant formation takes place over hundreds to thousands of years (Gile et al, 1966; Birkeland, 1999) and occurs seasonally (Breecker et al, 2009), leading to clumped isotope temperatures that presumably reflect long-term averaged, and in many cases seasonally biased, environmental temperatures (Peters et al, 2013; Huntington and Lechler, 2015; Burgener et al, 2016; Gallagher and Sheldon, 2016; Gallagher et al, 2019; Huth et al, 2019; Kelson et al, 2020). The origin and time-integration of geogenic carbonate isotopic compositions may be more difficult to ascertain.…”

Late Pleistocene Climate and Dust Source From the Mobarakabad Loess–Paleosol Sequence, Northern Foothills of the Alborz Mountains, Northern Iran

“…Soil carbonate isotope studies of modern soils and paleosols have typically focused on samples collected from temperate or warm environments (e.g., Quade et al, 2007;Hough et al, 2014;Diaz et al, 2016;Gallagher and Sheldon, 2016;Ringham et al, 2016;Bayat et al, 2017;Dietrich et al, 2017). The carbon and oxygen isotope composition of pedogenic carbonate (δ 13 C pc and δ 18 O pc ) and land snail shell carbonate within successions of rapidly buried Quaternary soils exhibit stratigraphic trends that are interpreted to record a history of significant climate variation and provide an additional technique for investigating Quaternary climate and ecologic changes (McDonald and McFadden, 1994;Monger et al, 1998;Lechler et al, 2018;Huth et al, 2019;Újvári et al, 2019Zamanian et al, 2021). Recent studies suggest a strong summer seasonal bias in some (Breecker et al, 2009;Passey et al, 2010;Quade et al, 2013;Huth et al, 2019) but not all pedogenic carbonates (Peters et al, 2013).…”

Sand calcites as a key to Pleistocene periglacial landscapes

“…These could show hiatuses correlated with glacial events like Dansgaard-Oeschger events or even record global minor or trace elements, as do ice cores and speleothems (Genty et al, 2003;Wainer et al, 2011). Such records would complement the range of published paleoclimatic archives from studies of speleothems (e.g., Villars cave; Genty et al, 2003;Wainer et al, 2011), pedogenic carbonates (Oerter et al, 2016;Huth et al, 2019), and lake levels (Blard et al, 2011;Hudson et al, 2015).…”