Oxygen isotopes in cellulose from modern and quaternary intertropical peatbogs: implications for palaeohydrology

Cellulose δ18O-values were measured in modern peatbog plants, in recent peats and in mountain peatbog cores from Burundi in a study of the hydrologic control of the |frsol|18O/16O ratio in intertropical peat cellulose. plants and waters were collected under various altitudes (800–2500 m a.s.l.) with mean annual relative humidity ranging from 0.72 to 0.82. The water δ18O-values (δi) vary between −4 and −2.5‰. The cellulose-water enrichment is of +25.3±0.5‰ for aquatic plants, of +24.6 emergent plant species. The scatter in the cellulose σ18O-values (δin) vary between −4 and −2.5‰. The cellulose-water enrichment is Cellulose δ18O-values of emergent plantss tend to decrease with increasing elevation (−0.6 to −0.07‰ per 100 m) and relative humidity (−0.5 to −0.1‰ per %). Mean emergent plant δ18O-values are approximated within ±0.6‰ by available cellulose δ18O models relating cellulose δ18O to the relative humidity (h) and the environmental water δ18O, except in a large swampy system. were subsampled in core Ka-2 (Kashiru, Burundi, 3°28′S, 29°34′E, 890 cm long, 2240 m a.s.l. altitude) and, for control, in the topmost 50 cm of core Ku-2 (Kuruyangwe, 3°35′S, 29°41′E, 2020 m a.s.l. altitude). Similar δ18O-vaues (+26 to +28.5‰) were found in the topmost 50 cm of both cores. They compare well with the mean δ18O for modern emergent plants at Kashiru. AMS-14C dating showed that core Ka-2 spans the last 30 ka. Celluloses are mainly derived from emergent plants and yield δ18O-values ranging from +19 to +29‰ with the highest values between 2.1 and 0 ka and the lowest values (+19 to +23.5‰) between 6 and 4.5 ka. For the period between 6 and 4.5 ka, the models yield a decrease in δin of −4 to −2.5‰ relative to present, for an h increase of 6% to 11%. Before 11.7 ka, the models yield a δin-value close to the present value, for an h increase of 6%.