We present a high resolution sedimentary record of dinoflagellate cysts spanning the last 900years recovered from Effingham Inlet, a glacial fjord on the west coast of Vancouver Island, Canada. The combination of seasonal coastal upwelling supporting high levels of marine primary productivity in surface waters, together with restricted bottom water circulation in the silled fjord, fosters the preservation of laminated sediments in the inner basin of Effingham Inlet. Geochemical data are used to assess the sedimentary facies of the core, which is composed primarily of laminated units (50.2%) occasionally interrupted by "seismites" (39.5%) and homogenous units (10.2%). The chronology of the 2m-long core is based on varve counting and fifteen 14C dates, and is anchored by a seismite previously dated at AD 1946.The dinoflagellate cyst assemblages are diverse (total of 47 taxa), abundant (average concentrations of 102,900cystg-1 of dry sediment), and characterized by a proportionally equal contribution of autotrophic and heterotrophic cyst taxa in most samples. Overall, cyst assemblages are characterized by Operculodinium centrocarpum (36.2%) accompanied by Brigantedinium spp. (18.0%) and Dubridinium spp. (6.6%). Multivariate analyses are used to extract the dominant patterns of variability in autotrophic and heterotrophic dinoflagellate cyst assemblages separately, and help in identifying the temperature and primary productivity gradients encoded in the cyst sedimentary record in this particular estuary.Specific intervals identified in the dinoflagellate cyst record are interpreted to represent the local expression of the "Medieval Climate Anomaly" (from the base of the record, AD 1090 to 1230), the "Little Ice Age" (AD 1230 to late 19th century) and warming in the second half of the 20th century. The timing of these intervals are consistent with the regional paleoclimate and help constrain past climatic and oceanographic variability on the west coast of Vancouver Island. The origin of homogenous units in the sedimentary record of Effingham Inlet and paleoseismicity in the region are also discussed.
Bibliographical noteFunding Information:
We are grateful to the officers and crew of the CCGS John P. Tully for their help during the sampling. Financial support for this research was provided by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery grant ( 224236 ) to V. Pospelova and the Canadian Foundation for Climate and Atmospheric Research (CFCAS) to S.E. Calvert. M. Bringué was supported by the Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT) B2 doctoral fellowship, the University of Victoria Bob Wright Graduate Scholarship, and Commander Peter Chance MASC Graduate Fellowship. We also wish to thank M. Soon (University of British Columbia) for supervising the C, N, carbonate C and opal determinations, as well as Z. Sandwith and A. Lew for their help in processing the samples and mounting the microscope slides, and C. Nittrouer (University of Washington) for the loan of the Kasten corer. We are grateful to Dr. Fabienne Marret and one anonymous reviewer for their constructive comments that helped improve the manuscript.
- Laminated sediments
- Little Ice Age
- Medieval Climate Anomaly
- Primary productivity reconstructions
- Warming in the second half of the 20th century