Distributions of fatty acids in a stalagmite related to paleoclimate change at Qingjiang in Hubei, southern China

Fatty acids extracted from a subtropical stalagmite at Qingjiang in Southern China's Hubei Province were analysed using gas chromatography-mass spectrometry. These n-alkanoic acids range from C₁₄ to C₂₆ in carbon number, maximizing at C₁₆, with a second dominance at C₂₂. In contrast to the stalagmite analysed, the overlying soils are characterized by the dominance of heavy-molecular-weight homologues (>C ₂₀). The n-fatty acids in the stalagmite were proposed to be contributed by both the soil ecosystems and the microbes harboring in the percolating water and the cave. The ratios of unsaturated to saturated n-fatty acids (C_16:1/C_16:0, C_18:1/C_18:0) appear to show trends comparable with the oxygen isotope records of the stalagmite carbonate, with enhanced values associated with the cold episode such as Heinrich event 1. This paleoclimate-dependent record of the n-fatty acids might reflect microbial changes in physiology and activity in response to the temperature. This record shows somewhat difference from the previous paleoclimate signal extracted from n-alkanols and n-alkan-2-ones of the same stalagmite. The acid record fails to document the well-known Younger Dryas event which was effectively shown by the latter two biomarkers derived from soil ecosystems. This discrepancy might result from the changing biogeochemical impact on different lipid fractions as well as the varied organism populations in different ecosystems. Copyright by Science in China Press 2005.