A 12,000-year dinoflagellate cyst record on the Vancouver Island margin, Canada: tracing past climatic, primary productivity and oceanographic conditions

Abstract

This is the first study to investigate dinoflagellate cyst records spanning the latest Pleistocene to the late Holocene on the Vancouver Island margin. We identified 14 autotrophic and 26 heterotrophic taxa, and defined four dinoflagellate cyst zones that were related to paleoclimatic and paleoceanographic conditions. Zone I (∼14–∼11.6 cal kyr BP) showed the lowest primary productivity (PP), indicated by the lowest total cyst concentrations and fluxes, with Brigantedinium spp. dominant in assemblages. This was likely due to cooler conditions associated with glacial meltwater input and weak coastal upwelling. Zone II (∼11.6–∼10.6 cal kyr BP) showed a slight increase in concentrations and fluxes of total cysts, a rapid increase in Operculodinium centrocarpum sensu Wall and Dale 1966 and the highest Nematosphaeropsis labyrinthus abundances. This zone was likely linked to reduced meltwater input and increased coastal upwelling, promoting primary productivity. Zone III (∼10.6–∼8.2 cal kyr BP) showed a rapid increase in PP, as demonstrated by maximum concentrations and fluxes of total cysts and autotrophic taxa abundances. This interval was interpreted as reflecting the strengthened California Undercurrent and increased upwelling, coinciding with the highest insolation intensity. High Impagidinium abundances during this time indicated more open ocean conditions. A sharp increase in Operculodinium centrocarpum–short processes during ∼9–8.2 cal kyr BP may be related to the 8.2 ka event and decelerated sea-level rise. Zone IV (∼8.2–∼2.3 cal kyr BP) suggested gentle fluctuations in PP, with overall declines of total cyst concentrations and fluxes, reaching the lowest at ∼8.0 cal kyr BP, followed by a slight increase at ∼6.5 cal kyr BP, and subsequent stabilization.