169S Prospectus


Paleoenvironmental Investigations

Continuous coring through the Holocene sediments offers the rare opportunity of sampling at a seasonal resolution both terrestrial and oceanographic temperate latitude changes over the past 10,000 -12,000 yr. There has been considerable interest expressed in being able to continue these investigations back through to deglaciation to understand better the succession of floras in this wet temperate region following deglaciation, climatic cyclicity during the Holocene, and the links among oceanographic, climatic, and terrestrial environmental conditions. Previous studies have looked at modern processes controlling the accumulation of diatoms in Saanich Inlet (Sancetta, 1989), at the annual cycle of sedimentation in the fjord (Sancetta and Calvert, 1988), and at various other aspects of faunal (e.g., changes in fish communities; V. Tunnicliffe, pers. comm. 1995) and terrestrial flora (R.J. Hebda, pers. comm., 1995). Other signals, such as the prevalence of fire and the human occupation of coastal sites, have also been detected in piston cores.

The Saanich Inlet sediments offer a unique opportunity to develop one of the world's most detailed, possibly continuous, Holocene, paired terrestrial and marine paleoecological records. These records will provide critical insight into the relationship between long- and short-term environmental fluctuations on land and sea and their link to climatic and other factors. In particular, detailed studies of inter- and intra-annual characteristics of the well-documented early to middle-Holocene warm and dry interval (Hebda, in press) may shed light on the potential impacts of global climate change in marine and adjacent coastal systems.

The objective of the interdisciplinary investigation is to develop an ultra-high-resolution paleoecologic record of the inshore northeast Pacific Ocean for the last 10,000 yr using organic remains preserved in Saanich Inlet sediments. This sequence would be related year-by-year to a 9000 yr tree-ring climate record and regional terrestrial environmental framework that has been developed for a lake site only 5 km distant on climatically sensitive southeast Vancouver Island (Hebda, in press).

Building on several decades of research, a small Joint Global Ocean Flux Study (JGOFS) project is being completed on annual and seasonal carbon accumulation and microfossil characteristics for the last century and a half in the inlet. This project has

So far Saanich Inlet sediments have proven to be extremely sensitive to recording even relatively minor events, such as the establishment of a small saw mill in the 1800s. Both the tree-ring and the annual layered-sediment series extend for millennia into the Holocene (Heusser, 1993; Hebda, in press).

Specific goals of a study of the complete Holocene record from Saanich Inlet are to


Driven by the concern that a great subduction earthquake or major crustal earthquake in southwestern British Columbia or northwestern Washington could cause widespread damage, several investigators have focused their attention on the geologic record for evidence of past events that could provide insight into the frequency and magnitude of future earthquakes. The paucity of large earthquakes within historical time in the region has required researchers to search for proxy data in order to ascertain whether such events have, in fact, occurred and, if so, with what frequency. Because of the remarkable stratigraphic preservation and resolution in the Saanich Inlet sediments, several recent studies have been undertaken focusing on the more silty massive units in the sequence as possible indicators of past earthquake events (e.g., Bobrowsky and Clague, 1990; Bobrowsky et al., 1993; Blais, 1992). These units have been interpreted as seismically triggered sediment gravity flows and, in the uppermost part of the sediment column (last 1500 yr), would indicate an average of one flow every 100 yr (Blais, 1995); this estimate appears compatible with projections made from historical seismicity data and are compatible with the rate of liquefaction events seen in Pleistocene lake deposits 100 km to the south in Washington State (Sims, 1975). Based on other evidence from the region, larger earthquakes (greater than magnitude 8 and believed to be of subduction origin) have a return period of about 600 yr. Clearly, however, to date neither the historical nor the geological records are sufficiently long to determine confidently the frequency of great subduction earthquake events or major crustal events.

Considerably more work is required to improve the confidence in this set of proxy data; much would be added by demonstrating that this rate has been consistent over a longer time interval, such as throughout the Holocene. A continuous record of seismically induced events over a long period would be an extremely valuable contribution to seismic hazard assessment in the region.

Sediment Diagenesis

Saanich Inlet has long been recognized as a model environment for studies of organic diagenesis and low-temperature remineralization reactions in a shallow, temperate, isolated, anoxic basin. The combination of restricted water circulation, seasonal stratification, and moderate rates of organic matter accumulation has led to dysaerobic bottom waters and anoxic sediments. This proposal is a good companion and comparative site to the ODP drilling of Santa Barbara Basin on Leg 146.

Benchmark studies were undertaken more than 20 yr ago (e.g., Gross et al., 1963; Gucluer and Gross, 1964; Nissenbaum et al., 1972; Presley et al., 1972; Brown et al., 1972). Saanich Inlet was selected for these studies for many reasons: (1) the sediments contain significant amounts of organic carbon (up to 5%), making it a possible recent analogue of black shales; (2) high sedimentation rates (4-5 times faster than in Santa Barbara Basin, for example) enabling detailed studies of early diagenetic processes; and, (3) two distinct sources of organic material, humus-rich soil from highly forested areas around the inlet and phytoplankton, primarily diatoms. Studies looked at major, minor, and trace element concentrations in interstitial waters and various sediment fractions, dissolved carbon dioxide, phosphate, sulfate, methane and ammonia, carbon isotopes, various hydrocarbons, and amino, humic, and fulvic acids. Most of these investigations, however, focused only on the upper 2 to 3 m of the sediment column.

Several geochemical factors make Saanich Inlet particularly attractive as a drilling site for ODP. The broad spectrum of diagenetic stages, including aerobic through to sulfate reduction and methanogenic fermentation, are represented and well characterized in the various Saanich Inlet sediments. Climatic variations during the Holocene (see above) are intricately recorded in the sediments as varvelike sedimentary structures. In addition to the sedimentologic evidence, initial organic and stable isotope geochemical investigations suggest that the signals of seasonal and climatic changes are faithfully recorded in the sediments. Significant climatic and redox shifts are recorded in Saanich Inlet sediments, enabling isotopic and molecular biomarker studies of proxy signals. Furthermore, long-term geochemical and ocean chemical measurements in Saanich Inlet have been made of the dissolved and particulate constituents in the water column and in the uppermost 3 m of sediment. These determinations, which include nutrients, gases, and inorganic solids as well as intensive surveys of biological populations, are distinct advantages of the location. Analysis of sediments from Saanich Inlet affords a unique opportunity for microbiologists and geochemists to provide detailed work on diagenesis of deeper seated sediments. Previously, most of the microbial work has been severely compromised by standard ODP operating conditions, such as (1) long periods at sea without shore laboratory contact (difficult to send critical fresh samples to shore-based labs) and (2) insufficient facilities available or accessible aboard JOIDES Resolution for specialized work-up of bacterial cultures, unstable compounds, and certain tracers.

These reasons make Saanich Inlet extremely well suited for advanced research in marine biogeochemistry. This is especially true for the investigation and application of molecular and stable isotope techniques to biomarker molecules as proxy signals to assess climatic changes. The drilling at this site is also a superb biogeochemical opportunity to investigate the microbial processes of methanogenesis and methylotrophy. Again, the site offers a unique chance to investigate organic compound classes, such as lipids and amino acids, and their response to changing redox and climatic conditions.

Saanich Inlet is also a rare and fundamental opportunity for marine microbial ecologists to obtain deeper sediment samples with which they can investigate the activities and processes of bacterial assemblages. Previously, this aspect of the ODP program has been restricted because of the special space and laboratory requirements of the biologists (e.g., radio-labelling, rapid access to microbiological laboratories); the drilling sites in Saanich Inlet, however, are very close to both federal and provincial government laboratories and to the University of Victoria. In addition, the requirement for rapid and frequent transport of samples from JOIDES Resolution (e.g., for shore-based incubations, gene probes, enzyme assays) has previously hampered and limited ODP-related microbiological work. Again, the location of Saanich Inlet has significant advantages in these respects.

To 169S Operations Strategy

169S Table of Contents

Publications Home

(ODP Home)