A team of scientists at China University of Geosciences, collaborated with researchers from University of Birmingham and William Paterson University, reported the first analysis of carbon isotope of fatty acids from stalagmite collected from Heshang Cave, central China. Their findings were published in the journal of “Earth and Planetary Science Letters” entitled “Speleothem Biomarker Evidence for a Negative Terrestrial Feedback on Climate During Holocene Warm Periods”.
Understanding how terrestrial carbon storage feeds back on warm climate states is critical for improving global warming projections. However, laboratory and mesocosm experiments to interrogate the response of soil carbon to climate change show highly variable results. Moreover, laboratory and mesocosm experiments have limited ecosystem complexity and operate on limited timescales, from years to decades. Thus, the longer-term climate sensitivity of soil organic matter and global soil carbon stocks, at the whole ecosystem level, is still subject to debate.
Stalagmites are important archieves for palaeoclimate reconstruction. Wang et al. obtained the first carbon isotope record of fatty acids from stalagmite over the past 9000 years trying to investigate the terrestrial feedbacks to warm climate in a longer time scale. They firstly reconstructed the vegetation changes using the carbon isotope of terrestrial derived C24 fatty acid. The vegetation showed a relatively increased proportion of C3 plants during the Holocene Climate Optimum (HCO) and Medieval Warm Period (MWP). More importantly, their study finds that soil bacteria selectively degrade more labile (13C-enriched) substrates during warm periods of the Holocene, suggesting that gross primary production outpaced soil respiration under higher temperatures. Their findings therefore show that soils in subtropical karst settings may represent a net carbon sink during warmer climate states, thus acting as a negative feedback on Earth’s climate.
Fig. 6. Vegetation changes and soil bacterial heterotrophic selectivity and respiration rates in response to climate changes. a, Compound specific δ13C values measured on the n-C16, n-C18, n-C22, n-C24 fatty acids extracted from the HS4 stalagmite. b, Variation in δ13C18FA(B) over the last 9 ka BP with locally weighted scatterplot smoothing of 25% (LOWESS). c, Acid-soluble organic matter (ASOM) carbon isotope (δ13CASOM) sequence derived from HS4 stalagmite (grey line) and three-point running average (red line) (Li et al., 2014). d, Temperature variation during the last 9 ka BP reconstructed by RAN15 from HS4 stalagmite from Heshang Cave, central China (Wang et al., 2018). e, Calcite δ18O of HS4 stalagmite over the past 9 ka BP (Hu et al., 2008b). U-Th dating errors (Hu et al., 2008b) are shown as black line segments.
Full Text from Publisher：https://www.sciencedirect.com/science/article/pii/S0012821X19304467
(Edited and translated from the Chinese version)
