A brGDGT‐Based Reconstruction of Terrestrial Temperature From the Maritime Continent Spanning the Last Glacial Maximum

Abstract

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 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‐year 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 and 34 ka indicate that Northern Hemisphere summer insolation may also influence land surface temperature in the IPWP region.

Reconstruction of warm-season temperatures in central Europe during the past 60 000 years from lacustrine branched glycerol dialkyl glycerol tetraethers (brGDGTs)

“…We tested several calibration models on our set of modern samples to assess their ability to produce temperatures that agree with instrumental temperatures. We used the CRU TS v4.01 dataset for modern temperature (representing the period 1901-2016; Osborn and Jones, 2014). We corrected for elevation differences at the five sample sites using a lapse rate of 6.6°C km −1 calculated from nearby meteorological stations (German Weather Service).…”

“…MAAT is for mean annual air temperature, and TMAF is for temperature of months above freezing. Temperature data refer to the 1901-2016 period from the CRU TS v4.01 dataset(Osborn and Jones, 2014).…”

Disentangling influences of climate variability and lake-system evolution on climate proxies derived from isoprenoid and branched GDGTs: the 250-kyr Lake Chala record

“…Modern system studies continued to highlight the relative importance of lacustrine brGDGTs production (Sinninghe Damsté et al, 2009;Tierney and Russell, 2009;Bechtel et al, 2010) and application of a soil calibration to lake sediments produced temperature estimates differing ∼10 °C from observations (Tierney et al, 2010b). Despite the strong correlation between MBT ′ 5Me in lacustrine surface sediments and temperature (Russell et al, 2018;Martínez-Sosa et al, 2021;Raberg et al, 2021), only few downcore applications of lake-based temperature calibrations since discovery of the 5-Me and 6-Me isomers have proved successful (Feakins et al, 2019;Stockhecke et al, 2021;Zhao et al, 2021;Zhang et al, 2021;Garelick et al, 2021;Ramos-Roman et al, 2022;Parish et al, 2023), partly due to uncertainties about the exact source(s) of brGDGTs in lakes. Recommendations to select temperature calibrations based on geographic region and/or mixing regime of the reconstruction site (Loomis et al, 2014b) are not strictly followed, and some studies use modified indices that seem better suited to the particular study site or reconstruction (e.g., Bittner et al 2022;Baxter et al 2023).…”