One hundred centuries of environmental change in Southern Vancouver Island

Saturday, November 23, 1996

What were the forests like on southern Vancouver Island, British Columbia at various times during the past 10,000 years? How have fish populations changed in the past in Saanich Inlet, a fjord north of Victoria. How frequent were forest fires in the region and how were they related to climate? How many major earthquakes have there been in the greater Victoria area since the glaciers left? What can past changes in climate and oceanography tell us about what we can expect for the future on southern Vancouver Island? These are just a few of the many questions which an international team of scientists will be trying to answer based on studies of long core samples of mud recovered during a two-day scientific expedition in mid-August this year in Saanich Inlet on southern Vancouver Island.

The specialized scientific ship, Joides Resolution, spent from August 19 to August 21 obtaining a continuous series of core samples up to 120 m long at each of two sites in the inlet. The sampling took place in the centre of the inlet, in water depths of 200 to 230 metres, near Brentwood Bay and immediately south of Patricia Bay. Saanich Inlet is uniquely suited to reconstruction of past environments on an annual, and even seasonal, basis because of the virtual absence of oxygen in the deep waters of the inlet. This condition means that many forms of animal life which would normally live on and beneath the seafloor, and churn it up as they move through and over it, are not present. Thus, we have preserved a precise layer-by-layer record composed of mud washed in by rivers, the remains of micro-organisms living in the water, pollen from plants around the inlet, plant fragments, fish scales and bones, and charcoal from forest fires, laid down since the glaciers left the area about 10,000 years ago. Each year is represented by a pair of light and dark layers, deposited on the seafloor during spring and summer, and fall and winter, respectively. In some instances, thinner laminae are also preserved within the annual pairs of dark and light layers probably related to flood events, sudden increases in oceanic productivity and, possibly, tidal conditions.

The highlights of the drilling program to date, based on visual examinations of the cores, include:

  • a complete record of annual, seasonal and even higher resolution environmental conditions, both terrestrial and oceanic, through the Holocene (last 10-12,000 years) and latest Pleistocene was obtained
  • lamina pair thickness (i.e., annual accumulation) varies from an average of about 6 mm to more than 1.5 cm
  • fish remains (mainly vertebrae) were found at several depths in cores from the two sites; wood debris and charcoal fragments were also recovered
  • there appears to be a cyclicity in lamina thickness and composition on a decadal to century time scale; the causes of these changes are not known at present
  • The Mazama Ash was found in cores from both drill sites; it appears as a white layer about 1 centimetre thick and was deposited 6,800 years ago from the eruption of Mount Mazama (Crater Lake, Oregon)
  • massive intervals several tens of centimetres thick are evident throughout the cores, interspersed with the finely laminated muds, and probably related to both earthquake-triggered underwater landslides and to periods of re-oxygenation of bottom waters
  • bottom waters immediately following the disappearance of glaciers from the region were apparently well oxygenated, as evidenced by the homogeneous character of the sediments and a well developed bivalve fauna
  • after an initial transition from clearly cold climatic conditions (glacial) to warmer (as seen in a change from gray, stiff muds to olive-coloured, progressively more laminated muds), there was a brief return to cold conditions before the final establishment of conditions similar to today; this brief return of colder conditions may correlate with similar episodes seen elsewhere in North America and Europe
  • glaciomarine sediments (deposited in the ocean under the influence of nearby glaciers) consist of stiff gray muds with some sand layers, chaotically bedded silts and sands and scattered very small pebbles relecting the presence of tidewater glaciers in the vicinity of Saanich Inlet; these sediments are older than about 12,000 years
  • 30 to 40 research scientists from 15 research organiza-tions were either onboard the Joides Resolution while it was in Saanich Inlet or will be working on the core samples in the coming months and years. Their specialities include chemistry, botany, zoology, microbiology (bacteria and viruses), geology, geophysics, oceanography, and climatology - a truly interdisciplinary team. Twenty-five Canadian scientists from universities across the country, from the Geological Survey of Canada, the Royal British Columbia Museum and the Geological Survey Branch of the British Columbia government are involved in the studies. Some of the core samples will remain at the Pacific Geoscience Centre of the Geological Survey of Canada in Sidney, British Columbia for one year to allow researchers in the region easier access for the detailed studies which will be undertaken. The remainder will taken to the Ocean Drilling Program's core repository in College Station, Texas

The ship is operated by the International Ocean Drilling Program, a scientific partnership of 19 countries, and contains the world's most advanced research equipment in operation at sea, housed in twelve laboratories. It sails with a complement of 115 scientists and crew. The Ocean Drilling Program is dedicated to the exploration of the history and structure of the ocean floor throughout the world. Canada has been a member of this consortium since 1985.

For Further Information on the Scientific Program:
Dr. Brian D. Bornhold Tel: (604) 363-6430
Pacific Geoscience Centre Fax: (605) 363-6565
Geological Survey of Canada, Box 6000
Sidney, British Columbia,
Canada, V8L 4B2

(Ed. note:) A description of ODP activities was given in WAT ON EARTH Vol. 5 No. 1 - not on-line, but available in hard copy