麻豆传媒

B.Sc. (Honours), Acadia University
M.Sc., 麻豆传媒

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 with the open ocean. Historical fish catch data suggest a large-scale expansion and contraction of this favourable habitat due to the large-scale changes in oceanic conditions that affect climate, i.e., upwelling and ENSO ( El Ni脩o Southern 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 (or oxygenation events), and the associated 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. 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 conditions in the innermost, restricted basin sediment cores, indicates that anoxic conditions predominate, but are not permanent. There are several discrete pulses of a marine, open water/shelf foraminiferal associations containing Buccella frigida, shadowed by an increased presence of the opportunistic, low oxygen-tolerant foraminifer, Fursenkoina fusiformis. These pulses or "events" are repeated several times, suggesting that there have been several incursions of fresh marine waters the last 4000 years into the inlet. These possible incursions are followed by episodes of high productivity triggered by the ephermeral introduction of oxygen and nutrients into the restricted basins. These episodes of high productivity in turn trigger anoxic conditions caused by the increased organic flux to the sea floor - all recorded by benthic foraminiferal assemblages.

The events mentioned above, particularly the open ocean events that may indicate upwelling, appears to occur at a similar periodicity (50+/- years) as historical records. This suggests that these upwellings and incursions may have been occurring at this frequency for the last 3000 yBP.

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Pages:聽 318
Supervisor: David Scott