Late Pleistocene temperature history of Southeast Africa: A TEX86 temperature record from Lake Malawi

摘要

We present a TEX_(86)-derived surface water temperature record for Lake Malawi that provides the first continuous continental record of temperature variability in the continental tropics spanning the past ~74kyr with millennial-scale resolution. Average temperature during Marine Isotope Stage (MIS) 5A was 26.5°C, with a range from 25.7 to 27.3°C, comparable to Holocene temperatures. MIS 4 was a relatively cold period with temperatures generally decreasing from 25.5°C at 68ka to a minimum of 20°C at ~60ka, 1.5-2°C colder than the Last Glacial Maximum (LGM). Termination of MIS 4 is characterized by a rapid increase of 3-4°C in only ~0.5kyr. Temperatures were relatively stable throughout MIS 3 at the resolution of this study, with an average of 23.8°C and a range from 25.1 to 22.9°C. The lack of millennial-scale temperature variability during MIS 3 suggests that Lake Malawi's documented response to the bipolar seesaw (Brown et al., 2007) is not reflected in its thermal history. Our temperature estimates for the LGM and Holocene are consistent with a previously published TEX_(86) record from Lake Malawi with a temperature of ~22.6°C for the LGM, ~25-26°C in the mid Holocene and ~25-28 for the late Holocene. In general the present extended TEX_(86) record indicates that temperature variability in tropical East Africa during late MIS 5 and MIS 4 was as great as that associated with the deglaciation and Holocene. A decrease in Southern Hemisphere insolation between 70 and 60ka may have played an important role in forcing temperatures during MIS 4, but after 60ka other factors, such as the extent of the polar ice sheets, or atmospheric CO_2 may have forced temperature in tropical Africa to a greater extent than local summer insolation.