NOAA/WDS Paleoclimatology - Martin Lake, Indiana, Long-Chain Plant Wax N-Alkane Hydrogen Isotope Data Over the Past 2000 Years

We compare hydrogen isotopic measurements of long-chain leaf-wax n-alkanes (δ2Hw; C27, C29, and C31) from Martin Lake, Indiana, USA, with a calcite-based reconstruction of the oxygen isotopic composition of precipitation (δ18Op) from the same lake. We observe stable and high δ2Hw during the Common Era (last 2000 years), which we interpret as growing-season precipitation originating mainly from the Gulf of Mexico and Atlantic. During the Little Ice Age (LIA; 1200–1850 CE), δ2Hw values increased by 3–8 ‰, concomitant with a significant decrease in δ18Op values by up to 12.5 ‰. Multiple proxy records for this time indicate persistent growing-season drought. We interpret these relatively high δ2Hw values, as compared to the δ18Op values, as a signal of low relative humidity that resulted in an 2H enrichment in plant source water resulting in high δ2H values through enhanced plant water and/or soil evaporation. These results support the occurrence of low humidity conditions during the LIA in the midcontinental USA that also contributed to the marked decline of regional pre-Columbian Mississippian populations.