Interannual variability of laminated sediment and its relationship to climate, Saanich Inlet, B.C.
Date
1997
Authors
Collins, Arlene Dawn
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
A test for proxy palaeoclimatic variations at high-resolution was carried out on two marine cores from annually-laminated anaerobic clay/biogenic sediment from Station 'E' in Saanich Inlet, British Columbia. The objective was to use sediment to reconstruct climatic parameters at seasonal-scale resolution for the southwest coast of Canada. A 133-year sequence (1860-1993 AD) of continuous, alternating light and dark layer couplets was measured and sampled at millimeter-scale resolution for total sediment, mineral detritus, opal, total carbon, organic carbon, carbonate carbon, calcium carbonate, total nitrogen and total sulphur.
Annual chronology was established from: (1) wood chips located only in lamina couplet years 1864-1879 AD. A lumber mill operated between 1863 and 1878 AD at a creek mouth on the inlet shore. Chips were washed into the basin during discharge initiated by winter precipitation, (2) pronounced 137 Cesium peak at couplet year 1964 (produced from atomic testing), and (3) elevated CaCO3 (%) values that reflect the activity of a cement plant on the inlet shore.
Laminae are composed mainly of mineral detritus and opal. Detritus arrives mainly from the nearby Cowichan River and predominates in both dark and light layers with average values of 74% and 66% by weight, respectively. Opal, the secondary component, reflects diatom production and increases on average from dark to light layers from 20% to 28% by weight.
Tests for associations between tree-ring widths from nearby Heal Lake and opal, porosity, total sediment, and total and organic carbon suggest that both systems may reflect some of the same climate forcing. Indices of the characteristics for the two cores show patterns of increases and decreases during the 133-year record. The seasonal and annual accumulation of sediment shows a rise around the late 1800s, a fall to around the 1920s, then a more recent increase in sedimentation rates after the 1960s. This pattern is reflected in extreme high, low, then high accumuJation rates of 0.53 g·cm-2.y-1 during 1888, 0.15 g·cm -2 ·y-1 during 1947, and 0.61 g·cm-2·y-1 during 1987.
Inlet sediment records a climate signal as determined from stepwise multiple regression tests upon instrumental climate data and sediment characteristics from 1900 to 1985. Cowichan River discharge, an indicator of precipitation, sea surface temperature, and intrusion into the basin of outside upwelled water, related to offshore wind stresses, yield significant coefficients of determination. These results offer insights into climatic controls during the years 1900-1985 AD and may aid the understanding of the entire Holocene sedimentary sequence from Saanich Inlet.