A 12,000-year record of dinoflagellate cysts from the Vancouver Island margin (NE Pacific): tracing past climatic, primary productivity, and oceanographic changes.

This study is the first to examine dinoflagellate cyst sedimentary records (core MD02–2496) from the latest Pleistocene to the late Holocene along the Vancouver Island margin (Li et al., 2025). We identified 14 autotrophic and 26 heterotrophic taxa and defined four dinoflagellate cyst zones related to paleoclimatic and paleoceanographic conditions. Zone I (~14–~11.6 cal kyr BP) showed the lowest marine primary productivity (PP), evidenced by the lowest total cyst concentrations and fluxes, with Brigantedinium spp. dominating the assemblages. This was likely a result of cooler conditions associated with glacial meltwater input and weak coastal upwelling. Zone II (~11.6–~10.6 cal kyr BP) displayed a slight increase in both total cyst concentrations and fluxes, alongside a rapid rise in Operculodinium centrocarpum sensu Wall and Dale 1966 and the highest abundances of Nematosphaeropsis labyrinthus. This zone was likely linked to reduced meltwater input and enhanced coastal upwelling, which promoted nearshore PP. Zone III (~10.6–~8.2 cal kyr BP) exhibited a rapid increase in PP, demonstrated by maximum total cyst concentrations and fluxes, as well as higher abundances of autotrophic taxa. This zone was interpreted to reflect a strengthened California Undercurrent and increased upwelling, coinciding with the highest insolation intensity. High abundances of Impagidinium during this time indicated more open ocean conditions. A sharp increase in Operculodinium centrocarpum with short processes around 9–8.2 cal kyr BP may relate to the 8.2 ka event and a deceleration in sea-level rise. Zone IV (~8.2–2.3 cal kyr BP) suggested gentle fluctuations in PP, with overall declines in total cyst concentrations and fluxes, reaching their lowest point around 8.0 cal kyr BP. This was followed by a slight increase at approximately 6.5 cal kyr BP, before stabilizing. After incorporating geochemical proxies from the same sediment core (Chang et al., 2008, 2014), we compared our findings with previously published reconstructions of climatic and oceanographic conditions along the western margin of North America. This comparison revealed spatial and temporal differences in marine PP and sea surface temperatures, especially between the northern and southern regions. Li, Z., Pospelova, V., Mertens, K.N., Chang, A.S., We, Y. 2025. A 12,000-year dinoflagellate cyst record on the Vancouver Island margin, Canada: tracing past climatic, primary productivity and oceanographic conditions. Palaeogeography, Palaeoclimatology, Palaeoecology, 667: 112876, 18 p. https://doi.org/10.1016/j.palaeo.2025.112876.Chang, A.S., Pedersen, T.F., Hendy, I.L. 2008. Late Quaternary paleoproductivity history on the Vancouver Island margin, western Canada: a multiproxy geochemical study. Canadian Journal of Earth Sciences, 45: 1283–1297. https://doi.org/10.1139/E08-038.Chang, A.S., Pedersen, T.F., Hendy, I.L. 2014. Effects of productivity, glaciation, and ventilation on late Quaternary sedimentary redox and trace element accumulation on the Vancouver Island margin, western Canada. Paleoceanography, 29: 730–746. https://doi.org/10.1002/2013PA002581.