What drives vegetation changes in South Sulawesi during the MIS 5e transition?

Sulawesi speleothem carbon isotopes (δ¹³C) are found to co-vary with deglacial warming and atmospheric CO₂ measured from Antarctic ice cores. This co-variation has thus far been attributed to speleothem δ¹³C recording changes in vegetation productivity and microbial activity in the soils overlaying caves as vegetation and microbes respond to glacial-interglacial changes in temperature and atmospheric CO₂ (Kimbrough et al., 2023; Krause & Kimbrough et al., in press). However, the relationship between speleothem δ¹³C and regional environmental change is complex and deconvolving the effect of different environmental drivers is difficult. To further investigate the ecosystem response in the Indo-Pacific Warm Pool to substantial warming and CO₂ rise during the penultimate deglaciation/marine isotope stage 5e (~127 kyrs ago) we use complimentary geochemical proxies extracted from stalagmite CaCO₃. These proxies include phosphorus and sulphur which respond to nutrient uptake by forest biomass above the cave (Treble et al., 2016). The relative abundance of metals such as copper, iron, zinc, and lead are assessed as another means to track biomass/soil regeneration via selective element delivery to the stalagmites by organic colloids flushed from the soil zone (Borsato et al., 2007). These vegetation proxies are compared with the speleothem δ¹³C and δ¹⁸O records and corresponding high-resolution fluorescence mapping of organics via confocal laser scanning (fluorescence) microscopy (Sliwinski & Stoll, 2021). The comparison of transition metals to stable isotopes (δ¹⁸O, δ¹³C) in the Sulawesi speleothem records makes it possible to distinguish between periods in the record where vegetation productivity increased in response to a rise in temperature and CO₂ verses periods where changing hydroclimate played a more dominant role. Characterising the appropriate drivers and proxy response is critical to accurately interpret tropical paleoclimate records where interpretations rely on assumptions that rainfall is the primary driver of vegetation change.

 

Kimbrough, A.K., Gagan, M.K., Dunbar, G.B., Hantoro, W.S., Shen, C., Hu, H., Cheng, H., Edwards, R.L., Rifai, H., Suwargadi, B.W., 2023. Multi-proxy validation of glacial-interglacial rainfall variations in southwest Sulawesi. Communications Earth & Environment, 4(210), 1–13.

Krause*, C.E., Kimbroug*, A.K., Gagan, M.K., Hopcroft, P.O., Dunbar, G.B., Hantoro, W.S., Hellstrom, J.C., Cheng, H., Edwards, R.L., Wong, H., Suwargadi, B.W., Valdes, P.J., Rifai, H., in press. Tropical vegetation productivity and atmospheric methane over the last 40,000 years from model simulations and stalagmites in Sulawesi, Indonesia. Quaternary Research.

Treble, P.C., Fairchild, I.J., Baker, A., Meredith, K.T., Andersen, M.S., Salmon, S.U., Bradley, C., Wynn, P.M., Hankin, S.I., Wood, A., McGuire, E., 2016. Roles of forest bioproductivity, transpiration and fire in a nine-year record of cave dripwater chemistry from southwest Australia. Geochimica et Cosmochimica Acta, 184, 132–150.

Borsato, A., Frisia, S., Fairchild, I.J., Somogyi, A., Susini, J., 2007. Trace element distribution in annual stalagmite laminae mapped by micrometer-resolution X-ray fluorescence: Implications for incorporation of environmentally significant species. Geochimica et Cosmochimica Acta, 71(6), 1494–1512.

Sliwinski, J.T., Stoll, H.M., 2021. Combined fluorescence imaging and LA-ICP-MS trace element mapping of stalagmites: Microfabric identification and interpretation. Chemical Geology, 581, 120397.