Proceedings of the 2007 Georgia Basin Puget Sound Research Conference
Session 3A: Ocean Observations
Chair: Brian Grantham
The Impacts of the Fraser Plume on the Optical Characteristics of the Strait of Georgia Waters, British Columbia, Canada
Light, along with nutrients and winds, in the waters of the Central Strait of Georgia affects primary productivity directly. The availability of light is however dependent on the many dissolved and particulate materials in the water, such as photosynthetic pigments, inorganic suspended matter, and chromophoric dissolved organic matter (CDOM). Upwelling radiance, downwelling irradiance, absorption, attenuation, CDOM and chlorophyll a fluorometric data, and suspended load were collected in the waters of Central Strait of Georgia in April and July 2006 along with oceanographic data for the purpose of identifying the influence of CDOM and suspended solids on the horizontal and vertical distribution of phytoplankton. The results show a significant spatial and vertical variability of the water on the Strait. Accordingly, the waters can be divided in three main optical classes: waters highly attenuated, with a strong scattering coefficient (closer to the Fraser); water with medium attenuation coefficients; and water with relative higher absorption due to phytoplankton (farther from the Fraser). These results indicate that the influence of the Fraser River on the light fields of the Strait of Georgia waters can be tracked by the optical variables in addition to regular oceanographic variable, such as temperature and salinity.
Nutrient Levels in Puget Sound: Decadal Changes and Controlling Factors in Regional Basins and the Strait of Juan De Fuca.
One of the greatest concerns for the Puget Sound ecosystem is nutrient inputs and subsequent negative impacts on water quality. Human and natural factors all contribute to nutrient loading. In some regions, loadings of nitrogen are significant enough for it to be considered a pollutant. Historically, scientists thought that nutrient concentrations would not increase enough to be a concern in the Puget Sound system. To assess this idea of unlimited capacity, seasonal and inter-annual nutrient concentrations for the past three decades are compared to historical values in the Main, South Sound, Whidbey and Hood Canal basins and the Strait of Juan de Fuca. Data to support this analysis is from the Department of Ecology’s ambient monitoring program where nutrient data is collected monthly from 40 core and rotational stations. In addition, datasets from intensive or seasonal surveys throughout Puget Sound are used. The use of nutrient levels as a measure in marine water quality and eutrophication indices will also be discussed.
Estuarine Versus Transient Flow Regimes in Juan de Fuca Strait
Residual currents in Juan de Fuca Strait are observed to switch between two fundamental states: estuarine and transient. The estuarine regime -- which prevails ~90% of the time in summer and ~55% of the time in winter -- has a fortnightly-modulated, three-layer structure characterized by strong (~50 cms-1) outflow above 60±15 m depth, moderate (25 cms-1) core-like inflow between 60-125 m depth, and weak (~10 cms-1) inflow below 125±10 m depth. Rotational effects increase the upper layer depth by 40 m on the northern side of the channel and upwelling-favourable coastal winds augment inflow in the bottom layer by as much as 5 cms-1. Fortnightly modulation of the estuarine flow by tidal mixing in the eastern strait leads to cross-channel “wandering” of the residual current such that surface outflow leads intermediate inflow by 180° at the fortnightly period. Transient flows -- which occur ~10% of the time in summer and ~45% of the time in winter -- are rapidly evolving, horizontally and vertically sheared “reversals” in the estuarine circulation forced by poleward wind events along the outer coast. Major events can persist for several weeks, lead to current reversals of 25 to 50 cms-1, and generate a net volume flux into the strait. A striking feature of major events is the formation of an O(10) km wide, surface-intensified, O(100) cms-1 inflow current along the southern boundary. This “Olympic Peninsula Countercurrent” is accompanied by an abrupt decrease in salinity indicating that it is a buoyancy-driven flow originating on the outer Washington shelf.
Remote Sensing of Chlorophyll-a in the Strait of Georgia
The Strait of Georgia is an important marine resource and is subject to significant anthropogenic forces. Satellite imagery can be a valuable tool for monitoring the Strait and its associated biophysical processes. As an important step towards this goal, an algorithm must be developed to estimate dominant optical constituents from ocean colour imagery in the Strait. This developed algorithm incorporates known optical properties of various constituents to estimate the influence of each on measured water colour. To evaluate the effectiveness of the developed algorithm, in situ radiometric and biophysical measurements collected during three research cruises carried out in winter, spring, and summer of 2006 were used. During the cruise, chlorophyll-a concentrations ranged from 1.9 to 25.0 ug l^-1 and total suspended solids ranged from 1.1 to 22.0 mg l^-1. This data set allows the chlorophyll-a algorithm to be evaluated against the range of conditions found in the Strait, including varying influence from terrestrial environments.
VENUS: A Cabled Ocean Observatory in Saanich Inlet and The Strait of Georgia
The Victoria Experimental Network Under the Sea (VENUS) is a cabled ocean observatory, with arrays in both Saanich Inlet and the Strait of Georgia. The first leg was deployed in February 2006 with an observatory node at 100m depth in Saanich Inlet. The second, deeper (300 and 175m) array will be deployed in the Strait of Georgia during the summer of 2007. The cabled observatory allows for unprecedented power and bandwidth to and from instruments connected to the observatory “nodes”. Data is retrieved and available over the web in near real-time. Preliminary instruments include standard oceanographic devices such as CTDs and ADCPs, as well as inverted echo-sounders, broadband hydrophones, and user controllable pan and tilt digital cameras. Advanced systems under development include vertical profilers and a dedicated delta dynamics laboratory. The data archive and instrument access are provided through the VENUS web site (http://www.venus.uvic.ca/), where galleries can be searched and data products requested. An overview of the observatory infrastructure, some preliminary scientific results, and how new users can access the facility will be presented.
Spatial and Temporal Chlorophyll Distribution in the Straits of Georgia and Juan de Fuca
We investigate the spatial and temporal distribution of planktonic biomass along with some factors influencing its distribution within the Straits of Georgia and Juan de Fuca. These two straits are the main constituents of a large coastal estuary system on the southern coast of British Columbia. A large amount of freshwater enters the coastal basin, with the main source being the Fraser River, and drives a two-way estuarine circulation. Complex biological dynamics (responses to light, nutrients, grazing, etc) dictate complex biomass distribution. However, a unique data set from a relatively long duration (over 5 years) and systematic (every season, at the same 70 stations) sampling program allows us to accurately describe the chlorophyll distribution in both time and space within the coastal basin. Over the study area, the main features of the spatial distribution of chlorophyll are shown to be closely related to variations in upper water column stratification. In addition, it is shown that, during the summer, plankton growth is nutrient limited within the central Strait of Georgia. Finally, the possible role of light limitation of the plankton production within Juan de Fuca Strait is discussed.