Naslov
Pedogenic carbonate nodules as seasonal paleoclimate archive

Autori
Šušnjar, Josip ; Domínguez-Villar, David ; Bensa, Aleksandra ; Švob, Mirna ; Krklec, Kristina

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Proceedings of INQUA SEQS 2021 Conference / Ratajczak-Skrzatek, Urszula ; Kovalchuk, Oleksandr ; Stefaniak, Krzysztof - Wrocław : University of Wrocław & Polish Geological Society, 2021, 109-109

Skup
INQUA SEQS 2021 "Quaternary Stratigraphy - palaeoenvironment and humans in Eurasia"

Mjesto i datum
Wrocław, Poljska, 13.12.2021. - 13.12.2021

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
pedogenic carbonates, nodules, thermodynamic model

Sažetak
Pedogenic carbonates can form in wide range of climates. They precipitate from supersaturated soil solutions during dry periods when evapotranspiration exceeds rainfall. These solutions are impacted by the chemistry of rainwater that equilibrates with soil CO2, which is released by root and microbial respiration as well as by organic matter decay. Consequently, isotopic signature of pedogenic carbonates is highly influenced by climatic conditions present during their formation, and its study in carbonate nodules of paleosoils can be used to unravel changes in climate conditions during the geological record. The δ18O values of pedogenic carbonates are mostly related to the isotopic signal of meteoric water, while the δ13C signal reveals information about dominant vegetation cover at the time of their formation. However, the isotope signals represent only the conditions at the time of carbonate precipitation. So, it is key to understand any possible seasonal bias in the rate of pedogenic carbonate formation to prevent any misinterpretation of the data as paleoclimate indicators. We studied a 0.6 m deep Red Mediterranean Soil profile in Dalmatia (Croatia) having a calcic horizon at the bottom. Over the period of 3 months, soil temperature, soil water content, soil bulk electrical conductivity and soil air CO2 were measured at the location. Based on the data collected, a thermodynamic model was developed for dissolution and precipitation of calcite in the soil. According to the results, two phases can be distinguished. From mid-April to mid-July a stage dominated by calcite dissolution is present. In this period soil water content was still high and progressive rise in temperature caused CO2 to build up in the soil, eventually resulting in dissolution of calcite, including some of the previous pedogenic carbonates. From mid-July until the end of our record high temperatures caused a negative soil water balance and eventually leaded to supersaturation of the soil solution and precipitation of pedogenic calcite. In both stages temperature controlled indirectly the chemistry of the solution. During the first stage, rise in temperature enhanced the microbial activity and/or other processes that increased the concentration of soil CO2 and caused the dissolution of calcite. During the second stage, however, temperature resulted in a negative effect on soil water balance by enhancing evapotranspiration, which controlled the chemistry of the solution causing precipitation of pedogenic carbonates. This research proves that at our studied site dissolution and precipitation events of pedogenic carbonates are related to specific stages within the year. Although a full year was not modelled, preliminary monitoring results suggest that not one, but two cycles of precipitation (summer and winter) and dissolution (spring and autumn) can be identified in a year at the studied site. Our results highlight the importance of understanding site specific soil dynamics for interpreting isotope records from pedogenic carbonates. Thus, pedogenic carbonates might be useful archives of seasonality rather than average climate and environmental conditions of the past. Continuous monitoring and modeling studies at the studied site, together with isotope analyses on carbonate nodules, will allow us to identify the potential of isotope studies to characterize seasonality over full annual cycles.

Izvorni jezik
Engleski

Znanstvena područja
Geologija, Poljoprivreda (agronomija)

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