HIGH RESOLUTION SEDIMENTARY RECORD OF DINOFLAGELLATE CYSTS FROM EFFINGHAM INLET (BC, CANADA) OVER THE PAST MILLENNIUM

Effingham Inlet, located on the west coast of Vancouver Island, is a silled glacial fjord that contains a unique sedimentary sequence, predominantly composed of annually laminated sediments occasionally interrupted by homogenous and massive units. While some massive units termed “seismites” are interpreted as mass-wasting events triggered by seismic activity, the laminated sediments hold valuable information on variations in paleoceanographic and paleoclimatic conditions, on annual to millennial time scales.

Here we present a continuous, high resolution record of dinoflagellate cysts and geochemical indicators from core TULK001, a ~ 206 cm-long freeze core collected in Effingham Inlet inner basin. Geochemical data are primarily used to determine the core facies (i.e., identifying seismites and other unit types), whereas dinoflagellate cysts are used to reconstruct past variations in phytoplanktonic communities, which respond to changes in the environment.

The age model, constrained by fourteen ¹⁴C dates, four previously dated seismites and varve counts, reveals that core TULK001 spans the last millennium (~ AD 1070 to 1991). Thus, this record sheds additional light on the termination of the “Warm Medieval Period”, the “Little Ice Age” and the “20^th century warming” in the region.

Preliminary results indicate that dinoflagellate cyst concentrations are high (average of 102.9 10³ and up to 983.2 10³ cyst g^-1 of dry sediment) and reflect the elevated levels of primary productivity in the inlet. Cyst assemblages are dominated by a taxon of autotrophic affinity, Operculodinium centrocarpum (36.2 % on average), accompanied by Brigantedinium spp. (18.0 %) and other cyst taxa produced by heterotrophic dinoflagellates.

Amongst the five “dinoflagellate cyst zones” determined statistically, the most recent zone (1955 to 1991) shows the highest level of dissimilarity when compared to older assemblages, which is also confirmed by Principal Component Analyses of the cyst data. This indicates that phytoplanktonic communities of the late 20^th century are strikingly different from the preceding millennium. Variations in cyst assemblages over the past millennium reflect changes in primary productivity, upwelling and precipitations at decadal and centennial time scales.