S. H. 2004. A record of Late Pleistocene and Holocene carbon accumulation and climate change from an equatorial peat bog (Kalimantan, Indonesia): implications for past, present and future carbon dynamics.ABSTRACT: A 9.5 m core from an inland peatland in Kalimantan, Indonesia, reveals organic matter accumulation started around 26 000 cal. yr BP, providing the oldest reported initiation date for lowland ombrotrophic peat formation in SE Asia. The core shows clear evidence for differential rates of peat formation and carbon storage. A short period of initial accumulation is followed by a slow rate during the LGM, with fastest accumulation during the Holocene. Between $ 13 000 and 8000 cal. yr BP, >450 cm of peat were deposited, with highest rates of peat (>2 mm yr À1 ) and carbon (>90 g C m À2 yr À1 ) accumulation between 9530 and 8590 cal. yr BP. These data suggest that Kalimantan peatlands acted as a large sink of atmospheric CO 2 at this time. Slower rates of peat (0.15-0.38 mm yr À1 ) and carbon (7.4-24.0 g C m À2 yr À1 ) accumulation between $ 8000 and 500 cal. yr BP coincide with rapid peat formation in coastal locations elsewhere in SE Asia. The average LORCA (long-term apparent carbon accumulation rate) for the 9.5 m core is 56 g C m À2 yr À1 . These data suggest that studies of global carbon sources, sinks and their dynamics need to include information on the past and present sizeable peat deposits of the tropics.

Abstract.-Radiocarbon-calibrated amino acid racemization ages of 428 individually dated shells representing four molluscan taxa are used to quantify time-averaging and shell half-lives with increasing burial depth in the shallow-water carbonate lagoon of Rib Reef, central Great Barrier Reef, Australia. The top 20 cm of sediment contains a distinct, essentially modern assemblage. Shells recovered at depths from 25 to 125 cm are age-homogeneous and significantly older than the surface layer. Taxon age distributions within sedimentary layers indicate that the top 125 cm of lagoonal sediment is thoroughly mixed on a sub-century scale. The age distributions and shell half-lives of four taxa (Ethalia, Natica, Tellina, and Turbo) are found to be largely distinct. Shell half-lives do not coincide with any single morphological characteristic thought to infer greater durability, but they are strongly related to a combined durability score based on shell density, thickness, and shape. These results illustrate the importance of bioturbation in tropical sedimentary environments, indicate that age estimates in this depositional setting are sensitive to taxon choice, and quantify a taxon-dependent bias in shell longevity and death assemblage formation.

A re-analysis of sea-level data from eastern Australia based on 115 calibrated C-14 ages is used to constrain the origin, timing and magnitude of sea-level change over the last 7000 years. We demonstrate that the Holocene sea-level highstand of +1.0-1.5 m was reached 7000 cal yr BP and fell to its present position after 2000 yr BP. These findings are in contrast to most previous studies that relied on smaller datasets and did not include the now common conversion of conventional C-14 ages to calendar years. During this 5000 year period of high sea level, growth hiatuses in oyster beds and tubeworms and lower elevations of coral microatolls are interpreted to represent short-lived oscillations in sea-level of up to 1 m during two intervals, beginning c. 4800 and 3000 cal yr BP. The rates of sealevel rise and fall (1-2 mm yr )1 ) during these centennial-scale oscillations are comparable with current rates of sea-level rise. The origin of the oscillations is enigmatic but most likely the result of oceanographic and climatic changes, including wind strengths, ice ablation, and melt-water contributions of both Greenland and Antarctic ice sheets.

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