A 60,000 YEAR RECORD OF CLIMATE CHANGE FROM LAKE TULANE FLORIDA: COEVALITY WITH THE NORTH ATLANTIC DANSGAARD-OESCHGER EVENTS, HEINRICH EVENTS, AND BOND CYCLES

In an earlier paper (Grimm et al., 1993, Science 261:198-200) we identified peaks in pine pollen from Lake Tulane, Florida that were coeval with the Heinrich events. In that paper we suggested that pine peaks corresponded with five of the Heinrich events (H1–H5) and that an extra pine peak perhaps correlated with minor peaks in the lithic grains from DSDP 609 between H3 and H4. We also suggested that the pollen data indicated wetter and cooler climate in Florida during the Heinrich events.

Detailed analyses of a new core with 55 AMS radiocarbon dates indicate that the six Lake Tulane pine phases were, in fact, coeval with the six Heinrich events. Conventional radiocarbon dating of our original core did not reveal sudden jumps in age that occur at the bases of Tulane pine phases 3 and 4, which resulted in errors in our original age model. Although these jumps may indicate hiatuses in sedimentation, their coevality with the Laschamp and Mono Lake geomagnetic excursions suggests that they were owing to major variations in atmospheric ¹⁴C concentration.

The pine phases persisted for up to several thousand years and were terminated by Heinrich events. The intervening oak-prairie phases were coeval with the large Dansgaard-Oeschger interstadials (warm periods in Greenland) that initiated Bond Cycles, and the pine phases were coeval with the extended D-O stadials (cold periods in Greenland) that terminated Bond Cycles or with the entire period of stadials and diminishing interstadials that followed the initial large stadial.

Analysis of aquatic and wetland macrofossils indicates that lake levels were higher during pine phases, confirming our earlier interpretation that climate was wetter. However, numerical analyses of the pollen data suggest that climatic conditions during the Heinrich events were similar to the late Holocene, which was wet and warm. We therefore interpret the climate in Florida during the Heinrich events to have been wet and warm. Perhaps diminishment of thermohaline circulation during the Heinrich events reduced northward heat transport and warmed the subtropical western Atlantic and Gulf of Mexico.