The temperate region of Western Europe underwent dramatic climatic and environmental change during the last deglaciation. Much of what is known about the terrestrial ecosystem response to deglacial warming stems from pollen preserved in sediment sequences, providing information on vegetation composition. Other ecosystem processes, such as soil respiration, remain poorly constrained over past climatic transitions, but are critical for understanding the global carbon cycle and its response to ongoing anthropogenic warming. Speleothem carbon isotopic (δ13C) records from Western Europe are often clearly correlated to regional temperature reconstructions during the last glacial and the deglaciation, with exceptional regional coherency in timing, amplitude, and absolute δ13C variation.
In this seminar, I will show how deglacial variability in speleothem δ13C is best explained by increasing soil respiration, by combining multi-proxy geochemical analysis (δ13C, Ca isotopes, and radiocarbon) on three speleothems from Northern Spain, and quantitative forward modelling of processes in soil, karst, and cave. This study is the first to quantify and remove the effects of prior calcite precipitation (PCP, using Ca isotopes) and bedrock dissolution (open vs closed system, using the radiocarbon reservoir effect) from the speleothem δ13C signal to derive changes in respired δ13C over time. Our results robustly show that an increase in soil pCO2 (and thus respiration) is needed to explain the observed deglacial trend in speleothem δ13C. Thus, we show that speleothem δ13C records may retain information on local soil respiration, and allow its reconstruction over time.