Late Holocene geologic, oceanographic and climate history of an anoxic fjord: Effingham Inlet, west coast, Vancouver Island.

摘要

Sediments preserved in the inner basin of anoxic Effingham Inlet on the west coast of Vancouver Island, give a high-resolution record of about 4,000 years of deposition. Changes in productivity and precipitation in the inlet are represented in the sediments by varying thickness of diatom/terrigenous mud varves. Ocean and climate changes affecting the inlet over the late Holocene can be interpreted from upwelling events which oxygenate the bottom waters of the inlet, which are represented by ungraded massive muds intercalated within laminated sediments. Therefore, high rainfall and cooler temperatures are interpreted to have existed about 2,000 to 4,000 y BP, following warmer and drier conditions than today's, prior to about 4,000 y BP.; The depositional record is complicated by graded and massive intervals that are interpreted to be the result of significant (M > 7) seismic events, that occurred historically in 1946, and prehistorically about 4,000 y BP, and many other smaller seismic events. A sand bed, is interpreted to be the result of a tsunami traveling up Effingham Inlet about 2,000 y BP, perhaps not surprising along this tectonically active coast.; A total of thirteen oceanographic surveys of the inlet beginning in 1995, confirm the modern anoxic character of the inner basin, and dysoxic character of the outer basin. Upwelled, oxygenated shelf waters can at times flush both the inner and outer basins to varying degrees, with dysoxic/anoxic conditions returning within months. A major flushing event was recorded in 1999, at the end of the 1997–98 El Niño, and is evidence that Effingham Inlet is being affected by continental scale oceanic processes.; Fish remains, including intact identifiable scales and bones, were retrieved from throughout the sediment record. Ten fish species are represented in the sediments, and the preserved scale counts show a cycling of fish populations in the inlet throughout the past 4,000 years. Although it is unclear what the relationship is between cycling of fish populations and ocean and climate conditions of Effingham Inlet, results of this study show that a low sediment volume record of fish scales, recovered from a small diameter piston core, can give high-resolution information on fish populations and ocean cycles over the late Holocene.