Calibration and application of a new paleotemperature tool in lacustrine systems: TEX86 for continental paleoclimate reconstruction
The calibration of the TEX86 (TetraEther IndeX of tetraethers with 86 carbon atoms) paleotemperature proxy in lacustrine systems provides a new hydrologically independent paleothermometer, enabling high-resolution lake surface temperature reconstructions from large lakes. TEX86 is based on the relative abundance of cyclopentane containing membrane lipids (glycerol dialkyl glycerol tetraethers or GDGTs) of aquatic Crenarchaeota, a non-thermophilic Archaea. I have developed a calibration for the TEX86 paleotemperature proxy from a climatically diverse suite of globally distributed lacustrine systems (N=15). The results of this calibration show a strong linear relationship between TEX86 values and published mean annual and mean winter lake surface temperature. The TEX86 index appears to work best in large lakes, which are typically the best integrators of regional climate variability. Methanogenic/methanotrophic and hydrothermal Archaea are capable of producing some of the same isoprenoid tetraethers, and in certain cases can confuse the TEX86 signal.
I have applied TEX86 to lacustrine sediments from Lake Malawi, East Africa, to develop high-resolution paleotemperature records from the Last Glacial Maximum (LGM) to the present. I find a ∼4°C overall warming since the LGM, with temperature reversals of more than 2°C during the Younger Dryas (12.5 ka BP) and in the early Holocene (Fig. 1), possibly associated with the 8.2 ka climate event. The onset of warming in the Lake Malawi basin coincides with the BYRD oxygen isotope record of warming in Antarctica. While the range of temperatures observed in this record is not surprising, the timing of post-glacial warming, the thermal response to the YD, and the Holocene history of warming and cooling trends are providing important new insights into tropical climate dynamics on centennial to millennial scales.
Additionally I have produced a temperature record from Lake Malawi spanning the past
700 years at ∼ 50 year sampling resolution. This record shows an anti-phase
relationship with solar forcing and primary productivity records through much of the
record. In the past 100 years there is a strong coherence with solar irradiance and
atmospheric CO2 concentrations with the temperature record indicating a
possible shift in tropical climate response to external forcing.