The tropics exert enormous influence on global climate. Despite the importance of tropical regions, the terrestrial temperature history in the Indo-Pacific Warm Pool (IPWP) region during the last deglaciation is poorly constrained. Although numerous sea surface temperature (SST) reconstructions provide estimates of SST warming from the Last Glacial Maximum (LGM) to the Holocene, the timing of the onset of deglacial warming varies between records and inhibits determining the forcings driving deglacial warming in the IPWP. We present a 60,000-yr long temperature reconstruction based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) in a sediment core from Lake Towuti, located in Sulawesi, Indonesia. BrGDGTs are bacterial membrane-spanning lipids that, globally, become more methylated with decreasing temperature and more cyclized with decreasing pH. Although changes in temperature are the dominant control on brGDGTs in regional and global calibrations, we find that the cyclization of the brGDGTs is a major mode of variation at Lake Towuti that records important changes in the lacustrine biogeochemical environment. We separate the influence of lake chemistry changes from temperature changes on the brGDGT records, and develop a temperature record spanning the last 60,000 years. The timing of the deglacial warming in our record occurs after the onset of the deglacial increase in CO2 concentrations, which suggests rising greenhouse gas concentrations and the associated radiative forcing may have forced deglacial warming in the IPWP. Peaks in temperature around 55 ka and 34 ka indicate that Northern Hemisphere summer insolation may also influence land surface temperature in the IPWP region.

Key Points

We produced a 60,000-yr long temperature reconstruction based on brGDGTs measured in a lake sediment core from Sulawesi, Indonesia.

We separate the influence of lake chemistry changes from temperature changes on the brGDGT records to develop the temperature record.

The timing of warming in our record occurs after the onset of the deglacial increase in CO2, which suggests CO2 forced deglacial warming.

Plain Language Summary

The tropics play an important role controlling global climate because they export heat to higher latitudes. Even though the tropics are important, we do not actually know the primary control on tropical temperature. We created a 60,000-yr long record of temperature because this length of record spans large changes in the proposed controls on tropical climate (greenhouse gas concentrations and incoming solar radiation). We created a temperature record from a lake sediment core from Lake Towuti in Indonesia. Since sediment gradually accumulated in the bottom of Lake Towuti for over 60,000 years, we took one sample from the lake sediment core every 6 cm to give us one sample every 500 years. We measured different types of molecules that compose the outer protective barrier (membrane) of bacteria cells. The molecules in the membrane are different in cold than hot environments. We measured the abundance of hot-adapted and cold-adapted membrane lipids to determine the temperature in the past. The timing of warming after the last glacial period occurs after the onset of the increase in CO2 concentrations, which suggests rising greenhouse gas concentrations and the associated radiative forcing may be the dominant control on temperature over the past 60,000 years.