Abstract
Subtropical peatlands are globally rare yet potentially important long term carbon sinks. The geomorphic controls on peat accumulation rates and carbon storage remain poorly constrained relative to temperate and boreal systems. This study integrates peat stratigraphy, carbon stock assessment, sedimentation rate interpretation, and peatland geomorphology (derived from ground penetrating radar [GPR]) to identify the primary controls on carbon storage in Empodisma minus dominated peatlands on K`gari (Fraser Island), eastern Australia. Peat cores were collected from three geomorphologically distinct systems identified using GPR: Moon Point, a low relief peatland developed over coastal and marginal marine sediments; Dilli Swamp, a composite peatland formed within lacustrine basins and relict coastal deposits; and marginal sandy peat wet heath representing an incipient peatland system. Carbon stocks range from 380 to 560 Mg C per ha at sandy peat margins with average thicknesses <1 m, to 870 to 1,170 Mg C per ha at Dilli Swamp where peat thickness averages 3.3 m, and up to 1,200 to 1,660 Mg C per ha at Moon Point with an average peat thickness of 1.3 m. Sedimentation rates are uniformly slow relative to temperate peatlands, reflecting nutrient poor sandy substrates and unique hydrology; but vary spatially with basin architecture and accommodation space. High accommodation settings such as Dilli Swamp exhibit thicker peat profiles and more continuous accumulation, whereas low accommodation coastal settings at Moon Point show reduced long term accumulation, increased compaction, and evidence of episodic hiatuses likely associated with fire and drying phases during the Holocene. These findings demonstrate that carbon storage in subtropical peatlands is controlled jointly by geomorphic setting and sedimentation dynamics. Basin architecture regulates peat accumulation continuity and resilience, with low accommodation systems more susceptible to carbon loss under future changes in fire regime and hydrology. Effective peatland conservation must therefore explicitly incorporate geomorphological and sedimentation controls. sedimentation rates, accommodation space, geomorphic controls, peatlands