Long-term patterns of peat accumulation and organic matter decomposition in Costa Rican peatlands

Abstract. Tropical peatlands, compared to their boreal counterparts, are vastly understudied despite these ecosystems acting as a significant terrestrial carbon sink, sequestering 100–300 gigatons of carbon. In particular, the low number of field-based studies from Latin America and the Caribbean limits our knowledge of these important wetland ecosystems: across the tropical Panamerican region, peatland location, soil characteristics, inception ages, and carbon accumulation histories remain largely unknown. These datasets are needed to inform a mechanistic understanding of why peat develops in certain areas but not in others, both in terms of peat initiation conditions as well as the factors that enable peat to subsist over centuries and millennia. Here we present extensive, high-resolution laboratory datasets from 11 peat cores from four peatland types from Costa Rica (high-elevation, riverine, coastal palm swamp, and mangrove). A multi-proxy paleoecological approach was employed to shed light on the successional pathways and past conditions that have allowed for these peatlands to form, as well as to provide a first estimate of their carbon stock. The core characterization includes radiocarbon dating, loss-on-ignition, carbon and nitrogen content, and plant macrofossils. Fourier transform infrared spectroscopy (FTIR) was also used to assess changes in organic matter quality across sites and over time, ultimately to clarify the role of recalcitrant material in tropical peat accumulation. Overall, this research provides a basis for understanding long-term carbon accumulation within Caribbean tropical peatlands and is critical to advancing knowledge of the structure of tropical peatland systems.