A proxy for all seasons? A synthesis of clumped isotope data from Holocene soil carbonates

Aptian-Albian clumped isotopes from northwest China: Cool temperatures, variable atmospheric <i>p</i>CO<sub>2</sub> and regional shifts in hydrologic cycle

“…In contrast, the "semi-arid monsoonal" model shows a decrease in water storage in April resulting in a slight cool season bias. However, cool season biases tend to be much smaller in magnitude (less than 4 ºC) than warm season biases (as much as 24 ºC) (Kelson et al, 2020). Therefore, regardless of the interpretation of seasonal biases, our mean temperature based on clumped isotopes (14.9 ºC) suggests very cool conditions in the mid-latitude Asian continental interior during the Aptian-Albian.…”

“…The presence of vegetation (suggested by abundant root traces) may shade the soil surface from solar radiation. However, Burgener et al (2019) and Kelson et al (2020) found that this effect is rare, and samples for this study were collected from paleosol horizons deep enough (i.e., > 50 cm) to be buffered against the effects of radiative heating (i.e., Burgener et al, 2019). Seasonality of precipitation, evaporation, and evapotranspiration likely affects the degree to which a warm season temperature bias may occur.…”

“…Nodules for analysis were sampled from well below channel sands and surface paleosol horizons in outcrop (i.e., sampled from paleosol B horizons; Tabor and Myers, 2015) to help avoid potential surficial biases on carbonate (e.g., radiative heating in soil depths <50 cm; Burgener et al, 2019). Paleosols from which nodules are sampled are fine grained throughout the section which suggests suitability for clumped isotope-based MAAT interpretation (e.g., Kelson et al, 2020).…”

“…Numerous early studies have suggested warm season bias in soil carbonate formation and thus the Δ47-derived temperatures (Breecker et al, 2009;Passey et al, 2010). Recent work of Kelson et al (2020) suggests this may not always be the case for a number of reasons. The presence of vegetation (suggested by abundant root traces) may shade the soil surface from solar radiation.…”

Palaeo-environmental evolution of Central Asia during the Cenozoic: New insights from the continental sedimentary archive of the Valley of Lakes (Mongolia)

“…towards lighter δ 13 C and δ O values and drier conditions favor an excursion towards heavier δ 13 C and δ 18 O values (Richoz et al, 2017). Hence, variations in chemical weathering indicators (CIA, PIA and CIW) and in the δ 13 C and δ 18 O profiles of soil carbonates across a sedimentary succession can be used to trace and assess fluctuations in the climatic conditions that prevailed in the source areas and in the sedimentary basin at the time of sediment deposition, and during pedogenesis (Nesbitt and Young, 1982;Bahlburg and Dobrzinski, 2011;Fischer-Femal and Bowen, 2020;Kelson et al, 2020;Zamanian et al, 2021). The formation of soil carbonates is a highly complex process that can complicate the interpretation of their δ 13 C and δ 18 O isotopic values (Richoz et al, 2017), as global climatic trends may be overprinted by regional factors, such as contamination with detrital carbonates, dolomitization, meteoric diagenesis, maturation or oxidation of organic matter, dis-equilibrium conditions between atmospheric (or biogenic) CO2 and soil solution, evaporation, basalt hydrothermalism, etc.…”