ABSTRACT: A high-resolution pollen, diatom, and sedimentary record of Late Holocene climate variability from an anoxic fjord in the Seymour-Belize Inlet Complex, British Columbia.

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Abstract

Laminated sediments retrieved Frederick Sound, an anoxic marine basin in the Seymour-Belize Inlet Complex of the central mainland coast of British Columbia, archive late Holocene climate variability that is linked to changes in solar activity and the relative position and strength of the Aleutian Low pressure system. High-resolution (26-year) analyses of fossil pollen and diatom assemblages document a detailed climate history spanning from ca. 4200 to 1050 years before present (yr BP). Cupressaceae (likely Thuja plicata and Chamaecyparis nootkatensis) was the dominant taxon in regional forests throughout the span of the record, but a decline in abundance is observed between ca. 2950 and 2100 yr BP. It is postulated that a dry climate interval abruptly punctuated the otherwise wet conditions of the Late Holocene in the Seymour-Belize Inlet Complex and was the proximate cause of vegetation change at this time. Contemporaneous changes in diatom species abundances (namely Skeletonema costatum) suggest that the interval from ca. 3050 to 1800 yr BP was also relatively sunny. Time-series analyses (Morlet wavelet and spectral analysis) carried out on biogenic silica abundances in core sub-samples and on sediment grey-scale colour variability derived from X-ray scans of the core identify non-stationary cycles within the Gleissberg and DeVries-Suess sunspot bands and a period of relatively high sun activity between ca. 3100 and 1800 yr BP. Biogenic silica is correlated to changes in total diatom abundance and the alternation between bright and dark sedimentary sequences is thought to represent fluctuations in the average duration and magnitude of seasonal diatom blooms and/or fluxes in the amount of terrigenous input. This suggests that decadal to centennial-scale variations in solar activity impacted marine primary productivity and precipitation patterns in the Seymour-Belize Inlet Complex though modulation of the relative strength and position of the Aleutian Low pressure system. The period of high sun activity in the mid-Late Holocene may have caused the dry conditions detected in the micropaleontological record by promoting a regional weakening and westward migration of the Centre of Action of the Aleutian Low pressure system, a phenomenon previously documented during periods of solar maxima. This study demonstrates the utility of a multi-proxy approach to paleoclimate research and indicates that late successional coastal forests in British Columbia can respond to change in less than a century.

Bibliography of Canadian Geomorphology