Benthic foraminiferal assemblages in Effingham Inlet, a fjord of western Vancouver Island, British Columbia: Implications for Late Holocene paleoproductivity of the northeastern Pacific.

摘要

Scientific interest in the evidence linking oceanographic processes and fish population dynamics in Canada has increased since the highly publicized Pacific salmon collapse off the west coast of British Columbia and the collapse of the Atlantic cod fishery. To study this problem in a prehistoric context, Effingham Inlet, western Vancouver Island, British Columbia was chosen as a study site. This inlet is a 17-km long by 1-km wide fjord (with anoxic to dysoxic bottom waters) located at the apparent northern extreme of the California Current with a connection to the open ocean. Historical fish catch data suggest an expansion and contraction of this favorable habitat due to the changes in oceanic conditions that affect climate, i.e., the 3–7 year ENSO (El NiÑo Southern Oscillation) and 30–50 year NP-DO (North Pacific Decadal Oscillation), but up until now there were no prehistoric data to verify long term trends.; Foraminiferal assemblages can be used as proxies for paleoclimatic and paleoceanographic conditions such as temperature, oxygen, salinity, and organic matter (OM) production. Various combinations of these factors may indicate periods of enhanced and suppressed upwelling, oxygenation events associated with marine incursions into the fjord and associated changes in productivity. Once the paleoceanography of a region is understood, it may serve as a proxy for the suitability of a paleohabitat for particular pelagic fish species over time. The restricted nature of Effingham Inlet is an ideal primary study site with its deep basins, shallow sills, laminated sediments and low sediment oxygen content, which provide well preserved sedimentological and paleobiological records of upwelling and other ocean-climate events.; The presence of foraminiferal species tolerant of low-oxygen (microxic) conditions in the innermost, restricted basin sediment cores, indicates that while anoxic conditions may predominate, they are not permanent. There are several discrete pulses of a marine, open-water/shelf foraminiferal associations containing Buccella frigida (indicating an influx of oxygenated marine shelf waters), followed by an increased presence of the opportunistic, low oxygen-tolerant foraminifer, Fursenkoina fusformis. (Abstract shortened by UMI.)