Evidence in peat of Late Quaternary climate and sea level change, western Indonesia

Eighteen peat samples, collected from vertical profiles in the interior of four domed ombrogenous peat deposits in Indonesia, were radiocarbon dated to determine onset and rate of peat accumulation. Onset of peat accumulation appears to be due to the following: a change to a wetter climate, a rise in the water table, availability of a platform for peat, and a decrease in sediment influx. A decrease in the rate of peat accumulation indicates a decrease in biomass production, possibly due to a decrease in nutrient availability, or an increase in biomass degradation, possibly due to increased aerobic degradation as a result of a drop in the water table. The earliest onset of peat, ca 10 ka, was observed 120 km inland at ca 18 m elevation. Peat started to accumulate at the rate of 0.9 mm/yr and slowed down to 0.2 mm/yr 4.3 ka when the peat was 5.7 m thick. Three of the peat deposits lie closer to the coast (0--43 km) and closer to present sea level ([minus]3 to +7 m). Peat in these deposits started to accumulate 6--4 ka. The youngest deposit has accumulated peat at an average rate of 1.6 mm/yr for the full 6.5 mmore » peat thickness. The other two peat deposits started accumulating at a rapid rate of 5 and 6 mm/yr and then slowed to 1.2 and 1.7 mm/yr at 4.2 and 3.4 ka, when the peat was 3.5 and 7.5 m thick, respectively. None of the deposits show compaction of the lower part of the peat profile (autocompaction). The data indicates (1) a change to a wetter climate ca 10 ka when sea-level rise drowned about half the area of the Sunda and Sahul Shelfs and (2) a subsequent slight drop in sea level starting at ca 6 ka resulted in subaerial exposure of extensive coastal lowlands.« less