The oldest extant tropical peatland in the world: a major carbon reservoir for at least 47 000 years

Tropical peatlands in Southeast Asia cover ~25 million hectares and exert a strong influence on the global carbon cycle. Recent widespread peatland subsidence and carbon dioxide emissions in response to human activity and climate change have been well documented, but peatland genesis remains poorly understood. Unlike coastal peatlands that established following sea-level stabilization during the mid-Holocene, inland peatlands of Borneo are little studied and have no apparent environmental constraint on their formation. Here, we report radiocarbon dates from the Upper Kapuas Basin which show inland peat formation since at least 47.8 thousand calibrated radiocarbon years before present, ka. We provide a synthesis of new and existing peat basal dates across Borneo, which shows a hiatus in peat genesis during a cool and dry period from 30 to 20 ka. Despite likely peat degradation during that period, the Upper Kapuas is still exceptionally deep, reaching a maximum depth (determined from coring) of 18 m. Our best estimate of mean peat depth over 3833 km2 of the Upper Kapuas is 5.16 ± 2.66 m, corresponding to a carbon density of 2790 ± 1440 Mg C ha−1. This is one of the most carbon-dense ecosystems in the world. It withstood the glacial-interglacial climate transition and remains mostly intact, but is increasingly threatened by land-use change.