# Peatland inception and development across Kalimantan, Indonesia

## TL;DR

This study examines the formation and carbon storage of peatlands in Kalimantan, Indonesia, revealing how their development is influenced by historical climate and hydrological conditions.

## Contribution

The study provides new chronological data on peatland inception and carbon accumulation in Kalimantan using radiocarbon dating and Bayesian modeling.

## Key findings

- Coastal peatlands formed during the middle Holocene, while inland peatlands began in the late Pleistocene.
- Carbon accumulation rates were highest in the middle Holocene and declined in the late Holocene.
- Human-induced drainage has significantly accelerated carbon loss compared to natural decline rates.

## Abstract

The peatlands in Kalimantan exhibit diverse geomorphological characteristics, but their initiation timing and drivers remain unclear due to limited chronological data. Using 55 radiocarbon ages and Bayesian age‒depth modeling of 15 peat cores, we reconstructed the development and carbon accumulation histories of inland and coastal peatlands in West and East Kalimantan. Coastal peat initiation occurred during the middle Holocene, coinciding with postglacial sea-level high stands, whereas inland peat formation began in the late Pleistocene. Carbon accumulation rates peaked in the middle Holocene (coastal: 63–72 g C m−2 yr−1; inland: 53–89 g C m−2 yr−1) under stable hydrological conditions but declined in the late Holocene (coastal: 49–55 g C m−2 yr−1; inland: 58–63 g C m−2 yr−1). The total decline rate was insignificant, at approximately 0.68 Mt C yr−1. These findings indicate that a sustained water balance is crucial for long-term peat growth and carbon sequestration and that hydrological disruption reduces the carbon storage. The current decline in the carbon sequestration capacity of drained tropical peatlands in Kalimantan is 32.4 Mt C yr−1 (118 Mt CO2-eq yr−1) over a 40-year period, representing approximately 47.5 times the natural decline in carbon sequestration over the past 4000 years.

The online version contains supplementary material available at 10.1038/s41598-026-35152-x.