The challenge of the enigmatic tricolporate tropical pollen type: A case study from Sulawesi, Indonesia

Abstract

Any palynologist who has worked in the tropics has undoubtedly dealt with the frustration of trying to classify small, tricolporate pollen into meaningful taxonomic groups. While this is not a significant issue where coarse-scale identifications represent similar habitat indicators or "unknown" types are rare, it poses a problem when one of these "unknowns" overwhelm the record. This is the case with unknown “type 69” – a small, tricolporate pollen grain encountered within a 60,000-year sediment sequence from Lake Towuti in Sulawesi, Indonesia. This type comprises up to 35% of the pollen count for some Last Glacial Maximum (LGM) samples (highlighting its climatic sensitivity) but could not be identified by experts in the field. This study thus aimed to compare the metrics of “type 69” with reference pollen from Sulawesi to aid with its identification. In doing so, we present a pollen atlas of 63 maritime southeast Asian pollen types. Our results show that “type 69” aligns with metrics taken from Saurauia pollen. While detailed ecological data on Saurauia species in Sulawesi are lacking, they appear to favor higher elevations and riverbank settings, and are post-disturbance colonizers. Proliferation of this pollen type during the LGM is therefore linked to a combination of downslope range expansion of Saurauia species under a cooler climate and potentially, out competition of upland everwet forest taxa. This study demonstrates an approach to managing important unknown fossil pollen types in tropical records and, through the ensuing pollen atlas, provides a tool for progressing palynology in southeast Asia. Show more