Environmental history of northwestern Vancouver Island (British Columbia, Canada) during the Holocene: A high-resolution dinoflagellate cyst record from Kyuquot Sound

Abstract

Environmental changes over the Holocene were reconstructed based on the analysis of dinoflagellate cyst assemblages, their absolute abundances, and morphological changes in Operculodinium centrocarpum sensu Wall & Dale 1966 from 103 sediment samples collected from Core 2012002PGC133 in Tahsish Inlet (Kyuquot Sound), a fjord on the west coast of Vancouver Island (British Columbia, Canada). Eight accelerator mass spectrometry ¹⁴C dates indicate that the record spans the last 12 ka. The cysts are well-preserved, with assemblages displaying high diversity (37 taxa). Six dinoflagellate cyst assemblage zones were identified. Zone I is dominated by Operculodinium centrocarpum sensu Wall & Dale 1966, while subsequent zones (II–IV) are characterized mainly by cysts of heterotrophic species. The uppermost zones (V–VI) show increased abundances of autotrophic taxa. The dinoflagellate cyst record reflects regional and global environmental signals. The dominance of Operculodinium centrocarpum sensu Wall & Dale 1966 during the Younger Dryas corresponds to a lower relative sea level, indicative of marsh-like conditions or proximity to the inlet head at the core site. Increased heterotrophic taxa during the late Early and Middle Holocene suggests a rising marine influence due to RSL rise, possibly enhancing primary productivity through coastal upwelling. Reduced process lengths in Operculodinium centrocarpum sensu Wall & Dale 1966 around ∼8.7 cal kyr BP indicate an abrupt change in local environmental conditions. A sharp increase in absolute cyst abundances ∼2.2 cal kyr BP, primarily driven by Spiniferites spp., is proposed to be linked with climate- and tsunami-related mechanisms.