Climate change in the mid-latitudes of North America during the marine isotope stage 11

Orbital configurations during the Marine Isotope Stage (MIS) 11 are similar to those of today's interglacial period. Study on the climate of MIS 11 may provide information on the type and magnitude of modern climate variability that could be expected under non-anthropogenic conditions. We have obtained a high-resolution calcite speleothem record from Morril's Cave (aka Worley's Cave), eastern Tennessee. The chronology was determined by U-Th dates and stable isotopic analyses were done with a sampling interval of 0.5 mm. The sample was apparently deposited under equilibrium conditions. We thus interpret its stable isotope records, spanning continuously from ~400 ka to ~342 ka, in terms of climate and environmental changes at this mid-latitude location. The carbon isotope profile shows a step-wise increase of δ13C, shifting from approximately -12‰ in the middle of MIS 11 to -8‰ near the end of MIS 11 and then to -4‰ in MIS 10. This step-wise increase may indicate a wetting to drying climate shift near the end of MIS 11. In response to the climate change, it also suggests that C3 plants probably dominated in eastern Tennessee during MIS 11, while a major transition from C3 plants to C4 plants occurred in this region when the interglacial period terminated. The oxygen isotopic value gradually increases through the record, with oscillations following the local summer insolation. The record is consistent with marine and ice core records, but also featured with prominent millennial-scale variations, which suggests climate instability during the climate transition period.