MULTI-PROXY EVIDENCE OF MILLENNIAL CLIMATE VARIABILITY FROM FOUR BAHAMIAN STALAGMITES

Northern Hemisphere tropical paleoclimate records support significant hydrologic and climatic changes associated with Dansgaard Oeschger (D/O) events and Heinrich stadials 1 to 6. However, few absolutely dated terrestrial records from the western Atlantic span the last six Heinrich stadials. Here we present geochemical results from four stalagmites collected from a cave in the Bahamas which encompass Heinrich stadials 1 to 6. Absolute geochronometry using U-Th equilibrium series demonstrated that the stalagmites formed between 63.8 to 13.8 kyr before present. The δ¹³C and δ¹⁸O values of the calcite showed higher values associated with Heinrich stadials 1-6 and lower values during the D/O interstadial events. The δ¹⁸O value of fluid inclusions from one stalagmite demonstrated minimal variation in the formation water δ¹⁸O value during Heinrich stadials 1 to 3. The Sr/Ca ratios of the calcite are shown to be relatively invariant, while in two of the samples the Mg/Ca ratios tracked the δ¹³C values.

Increased calcite δ¹⁸O values across Heinrich stadials 1-6 are interpreted as being driven by lower temperatures, as supported by the fluid inclusion results. The two deeper occurring stalagmites demonstrate increased Mg/Ca ratios and δ¹³C values during Heinrich stadials 1 and 2 which are interpreted as a signal of reduced flow rates in the epikarst and increased water/rock interactions as a result of increased aridity which potentially occurred across all six Heinrich stadials. The observed reductions in mean annual temperature and amount of precipitation across Heinrich stadials are proposed to be driven by a reduction in sea surface temperatures in the North Atlantic and an expanded Bermuda High. During D/O interstadials, the Bahamas cave records likely indicate warmer and/or wetter climate; however the isotopic shifts are not as significant as the isotopic excursions associated with Heinrich stadials.