How does stuff wash ashore in the Salish Sea?

How does stuff wash ashore in the Salish Sea? The shores of the Salish Sea are covered in logs and trash ranging from large half-destroyed floats down to small pieces of plastic. How does it all get there? Over the past 6 years nearly 500 drifters, equipped with GPS to record positions with an accuracy of a few meters every 10-20 minutes, have been released in these waters (see drifters.eos.ubc.ca), and they have washed ashore more than 700 times. This resulted in plenty of interesting anecdotes, as tracks show a variety of surprising behaviors (including getting run down by ships). But, in addition, a statistical analysis was used to answer some interesting general questions about the Salish Sea. For example: where do things like to wash ashore? Can they escape the Salish Sea by going out into the Pacific? At what stage of the tide does stuff tend to run aground? What\u27s the probability of grounding for items floating 20, 50, or 100m offshore? What are ocean currents like near the shore? The answers to these questions may improve modelling and policy (and they are fun science)

Salish Sea surface currents: real-time velocities from HF radar

Ocean Networks Canada has operated Salish Sea CODAR high-frequency (HF) surface radar systems for monitoring surface currents since 2012. The network of antennae continues to grow, with four arrays now deployed in the southern Strait of Georgia, two more planned for the Strait of Juan de Fuca, and several more installed and planned along BC’s northern coast. These arrays provide hourly maps of surface currents. In the Strait of Georgia, where the Fraser River and ocean tides meet, there are complex surface current patterns that vary under seasonal river and wind conditions. Data are used to understand the circulation, validate model simulations, and could be used to assist in oil spill tracking and search and rescue efforts. An overview of the systems, the currents, data quality procedures, and future plans will be presented

Fate of diluted bitumen spilled in the coastal waters of British Columbia, Canada.

Abstract There is public concern about the behaviour of spilled diluted bitumen (dilbit) in marine and estuarine waters. We provide a preliminary assessment of the results of laboratory experiments and models, in the context of environmental conditions in the coastal waters of British Columbia. Most dilbit spilled within this region would likely float at the surface and be transported to shore by winds and currents. Fresh dilbit is too light to sink in coastal waters. Highly weathered dilbit could sink where salinity is less than 14, typically only near river mouths and in the top 1–3 m of fjords after heavy rainfall. Subsurface plumes of weathered dilbit could re-emerge at the surface. Sinking oil-particle aggregates are unlikely to form in coastal waters. However, dilbit could be entrained below the surface by wave mixing during storms and to depths of 150 m by coherent mixing in the Haro Strait tidal convergence zone

Observations and linear analysis of sill-generated internal tides and estuarine flow in Haro Strait

Current meter records from two sets of observations 20 years apart in Haro Strait, British Columbia, Canada, are analyzed. Haro Strait is a deep channel separated from larger bodies of water on either side by relatively shallow sills. The estuarine flow in this region is in approximate geostrophic balance and is apparently unaffected by the tidally driven spring/neap cycle in vertical stratification. Strong baroclinic variability with an amplitude 1 m s-1 (close to the amplitude of the barotropic tide) is present. A linear theory for internal tides in silled basins is developed using no-bottom-flow boundary conditions to represent sill effects. By comparison with observations it is concluded that an internal tide is generated at the seaward sill and propagates inshore. Although local damping appears to be weak, no return signal is found from the inshore sill, suggesting that either dissipation is strong in that area or that the internal tide is transmitted across that sill. An edited version of this paper was published by AGU. Copyright 2002 American Geophysical Union.Science, Faculty ofEarth and Ocean Sciences, Department ofReviewedFacult

Horizontal circulation in the Strait of Georgia

Quantitative estimates of the spatial mean estuarine circulation in the Salish Sea, over monthly and seasonal time scales are known reasonably well using a box-model view of the circulation. In this view, Strait of Georgia deep inflow waters have a northward speed of a few cm/s, and outflow currents near the surface have southward speeds of about 5 cm/s. However, actual measurements of the large-scale deep currents find subtidal speeds of more than 30 cm/s in some places, and current in the wrong direction in others. Long-term observations of currents from the ONC/VENUS nodes, as well as shipborne transects and drifter tracks, show that inflow waters hug the southeastern side of the Strait, often as a narrow boundary current which carries a volume flux considerably greater than that of the estuarine inflow. A broad return flow in the central and western Strait compensates for this. Near the surface, on the other hand, winds blow the surface water around and this dominates short-term predictability

Estuarine forcing of a river plume by river flow and tides

Estuarine forcing of a river plume by river discharge and tides is examined with a novel data set capable of characterizing semidiurnal to annual time scales. An instrumented ferry made high‐resolution salinity measurements as it crossed the Fraser River plume, British Columbia, Canada, eight times per day over the years 2003–2006. The relative contribution of different forcing factors in controlling the river plume salinity and surface area is examined over the full range of time scales. A Lomb‐Scargle periodogram of the plume salinity shows energy concentrated in the semidiurnal and diurnal tidal bands. Diurnal lines contain more energy relative to semidiurnal lines than the respective tidal constituents would suggest. At fortnightly frequencies, local maxima in plume salinity coincide with periods of maxima in daily tidal height, with no phase shift. Thus the estuary adjusts quickly to changes in forcing. The effectiveness of tides in setting the plume salinity is a function of river discharge and is greatest when the river discharge is high and minimal when the river discharge is low. Tidal effects are superimposed onto the long‐period river discharge cycle. At time scales of 25 days or longer, the mean river plume salinity decreases quasi‐linearly with increasing river discharge, but the change in salinity with river discharge is instantaneous to within the sampling resolution. Plume surface area increases with river discharge, from 200–500 km2 at low river flow to 1000–1500 km2 at high river flow. The magnitude of the surface area is predicted well by scaling the mouth deformation radius. An edited version of this paper was published by AGU. Copyright (year) American Geophysical Union. An edited version of this paper was published by AGU. Copyright 2008 American Geophysical Union.Science, Faculty ofEarth and Ocean Sciences, Department ofReviewedFacult

Double diffusion in saline Powell Lake, British Columbia

Powell Lake contains a deep layer of relic seawater separated from the ocean since the last ice age. Permanently stratified and geothermally heated from below, this deep layer is an isolated geophysical domain suitable for studying double-diffusive convection. High-resolution CTD and microstructure measurements show several double-diffusive staircases (R-rho = 1.6 to 6) in the deep water, separated vertically by smooth high-gradient regions with much larger density ratios. The lowest staircase contains steps that are laterally coherent on the basin scale and have a well-defined vertical structure. On average, temperature steps in this staircase are 4 mK, salinity steps are 2 mg kg(-1), and mixed layer heights are 70 cm. The CTD is capable of measuring bulk characteristics of the staircase in both temperature and salinity. Microstructure measurements are limited to temperature alone, but resolve the maximum temperature gradients in the center of selected laminar interfaces. Two different algorithms for characterizing the staircase are compared. Consistent estimates of the steady-state heat flux (27 mW m(-2)) are obtained from measurements above and below the staircase, as well as from microstructure measurements in the center of smooth interfaces. Estimates obtained from bulk interface gradients underestimate the steady-state flux by nearly a factor of 2. The mean flux calculated using a standard 4/3 flux law parameterization agrees well with the independent estimates, but inconsistencies between the parameterization and the observations remain. These inconsistencies are examined by comparing the underlying scaling relationship to the measurements

Satellite based study of wind and river forcing of the Fraser River plume

The Fraser River is the largest source of inorganic particles to the Strait of Georgia (SoG). Most of the particles escape the Fraser estuary and mudflats, and enter the SoG in a buoyant plume. The fate of these particles now depends on our understanding of how the plume responds to forcing by wind, river flow, and tides. The distribution of inorganic particles affects important processes such as light attenuation in the water column and adsorption of contaminants. Previous studies of particle dispersal in the SoG were based on light transmission profiles or sediment traps, and they lacked sufficient resolution in time and space to adequately address how the large and fickle Fraser River plume responds to forcing. Satellite imagery can overcome some of these sampling limitations. In this talk we present early results from an analysis of 13 years of satellite imagery of the SoG. Maps of suspended particulate material were derived from the application of a single-band algorithm utilizing MODIS HiRes band 1 (620 - 670 nm), which has a nominal resolution of 250 m. After validating the images with in situ optical and hydrographic data, we conditionally average the images to determine how the plume varies in response to river flow and wind conditions. Under calm winds, the plume occupies a larger surface area as river flow increases. Surprisingly, it undertakes a southward set under calm winds, contrary to the influence of rotation. Under northwesterly winds, the plume is advected southward, even reaching as far south as the San Juan Islands under strong winds. Under southeasterly winds the plume is advected to the northwest. However, it is important to point out that these are just average tendencies, and they are only somewhat representative of the myriad of shapes and sizes displayed by the plume