A New Paradigm: Cabled Ocean Observing System Research
VENUS is an advanced cabled ocean observing system. It represents the next generation of Internet ready tools for ocean exploration. Connecting ocean sensors and instrument platforms to an undersea network allows for real-time and interactive ocean research. Through standard Internet and Web connections, scientists and engineers from anywhere in Canada and around the globe can access, configure, and interact with network instrument systems. Data, signals, and images are relayed in real-time to researchers via the Data Management and Archiving System over the Internet on the Data Galleries. Scientists can detect environmental changes as they happen, monitor variations in the marine conditions, and respond to events. In addition to real-time data streams, maintaining a long term facility and archive will allow longer-term studies of seasonal, decadal, and climate variations in our complex coastal ocean environments.
VENUS in the Local Marine Environment
1. Is our local ocean warming?
Can we see changes in the physical properties and the chemical composition as a result? VENUS will provide a monitored, consistent extension to the periodic ship observations that show the seasonal and longer variations of our local waters.The long-term records produced by VENUS instruments are rare and the information and signals they will contain are vital.VENUS probes will measure temperature, salinity, seawater density, tides, and dissolved gasses.
2. How healthy are the transient and resident whale pods in the Strait of Georgia?
Historically the Strait of Georgia has supported both resident and transient Orca whale pods. In the last few years, the resident whales have periodically migrated as far way as northern California. Why? When? For how long? The VENUS hydrophones will monitor whale movement, record and allow us to better learn their vocabulary, and allow us to monitor their use of the southern Strait.
3. Is the ocean a quiet place?
Many processes can generate sound in the ocean. Atmospheric disturbances such as rain, hail, and wind all produce unique audible signatures. Human activities, most notably boat and ship engine noise, can produce persistent back-ground noise underwater. The VENUS hydrophone arrays will monitor the sounds in the Strait of Georgia, and allow researchers to identify natural and anthropogenic sound sources.
4. What is the ecology of the seafloor in the deeper regions of the Strait?
Most scientists study seafloor animals by dredging or occasional visits from submersibles. We know little about how the bottom habitat of Strait of Georgia is controlled by the swift, reversing tidal currents, sediment dumps from the Fraser, or overlying plankton blooms. VENUS is a unique opportunity to examine the adaptations of organisms to high flows. The facility may also give us those rare glimpses of large deep water animals. Scientists also plan studies of bottom community responses to large food falls such as carcasses.
5. How do tides and the Fraser River influence the marine ecosystem?
The physical and chemical marine habitat, as defined by the seawater temperature and salinity, and dissolved constituents such as oxygen and biologically important nutrients, under-goes significant variations over the annual seasons. What is the role of the tides in mixing oxygen rich, but nutrient poor surface water with the deep salty nutrient rich water? How does the Fraser River, which each spring drains the snow pack from southern BC, impact the health of the Strait? VENUS sensors near and above the ocean floor will monitor and allow studies into the Strait as a marine habitat.
6. What are the dynamics of the Fraser River Plume?
Near the Fraser River mouth, the surface water is brackish, a diluted mixture of fresh water and seawater. How deep is this layer? How far and what causes it to spread? When does it drift towards the south? North? In the summer, this brackish plume is also warm and nutrient rich. How important is it to local and remote ecosystems along our coast? VENUS will monitor the local dynamics and the temporal variations in the temperature and salinity near and within the Fraser River plume.
7. When and what causes deep water renewal in the Strait?
While the surface water is warm and fresh, the deep waters within the Strait are cold and salty. How deep do the tidal currents go? With the Fraser River putting out so much fresh water, why doesn’t the Strait become progressively more fresh? Where and when does salty water enter the Strait? VENUS sensors will monitor and explain the movement of both warm/fresh surface waters, as well as the cool/salty deep waters.
8. Are migratory (e.g. salmon) and resident (e.g. ling cod) fish populations sustainable?
Recent technology advances allow us to tag juvenile fish with acoustic beacons that allow for remote detection and identification. How long do young salmon stay in the Strait? Do they leave via Juan de Fuca or Johnstone Strait? We have started to protect certain rock-fish habitats, but over what range do rock-fish forage? VENUS will support a network of fish tag receivers to monitor tagged fish movement.
9. Where does all the sediment suspended in the Fraser River go once it enters the Strait?
The settling of river sediment slowly builds up the Delta, extending the mud-flats out into the Strait. Along the edge of the delta, the delta slope, the unconsolidated sediments form a steep cliff. Periodically the slope fails, and an underwater land slide ensues. What are the conditions before, during, and after such a dramatic event? What triggers a slide? What are the impacts of a slope failure on the local habitat? VENUS will have a dedicated suite of sensors and experiments monitoring and measuring the Delta Slope Stability.
Ocean Science Research on VENUS
Below are some of the science and research interests in both Saanich Inlet and the Strait of Georgia that will be served by the VENUS cabled ocean network.
Estuary Circulation and River Plume Dynamics
The Strait of Georgia is part of a large regional estuarine system where by relatively fresh surface waters, fed by river discharge, meander and mix with deeper more saline ocean waters in a steady flow towards to open ocean via Juan de Fuca Strait and Johnstone Strait. The largest river is of course the Fraser, which drains much of southern BC and spills thousands of cubic meters of fresh, sediment laden water into the Strait of Georgia every second. Despite this input, the Strait remains relatively salty, as a result of a continuous river of deep salty water that flows in along the bottom from Haro Strait and Boundary Passage. VENUS scientists will study the circulation and exchange processes associated with this estuarine circulation using measurements of: temperature, salinity, seawater density, dissolved oxygen, sea-level (pressure), currents, tides, and ocean mixing.
The ocean food chain consists of several trophic levels, including the primary producers, microscopic phytoplankton (floating algae), secondary producers, macroscopic zooplankton, and heterotrophic fish and mammals. Plankton refers to all drifting organisms, and the phytoplankton only grow in the upper ocean where light is available. Zooplankton, that feed on the phytoplankton, must also spend time in the surface waters where their food is, but will attempt to avoid visual predation by fish by swimming down into the dark depths during daylight hours. This diurnal migration can be monitored and quantified using high frequency inverted echo-sounders connected to the VENUS network.
Deep Water Renewal
At specific periods during the year, periodic deep water flows replenish the densest and deepest waters in the Strait of Georgia. Seawater density is primarily controlled by the temperature and salinity concentration of the water. Cold water is more dense than warm, and salty more dense than fresh. In the early spring/late winter, cold/fresh seawater enters the Strait at Boundary Passage and flows along the bottom towards the deep northern basin. In the late summer, warm/salty seawater flows into the basin. The winter renewal brings low nutrient/elevated dissolved oxygen seawater into the deep regions of the Strait, while the late summer renewal events bring high nutrient/low oxygen seawater into the basin. Both renewal processes provide important replenishment of deep water characteristics that sustain the ecosystems of the basin. VENUS will provide direct measurements of the magnitude and timings of these renewal events through near-bottom measurements of temperature, salinity, seawater density, dissolved oxygen, and ocean currents.
Marine Mammal Communications
Although coastal waters are murky and limit vision to several metres, sound propagates very efficiently over tens of kilometers. Marine mammals, such as Orcas rely heavily on vocalizations for communicating and finding food. Resident and transient pods frequent the Strait of Georgia, and understanding their “language” and use of active sonar is a central research project for VENUS. Mammal vocalizations will be monitored with precision broadband hydrophone arrays. However, the Strait is also a busy shipping corridor. How marine mammals react and adapt to the noise produced by ships is a key research topic. Streaming and archived audio from the VENUS hydrophone arrays will be available on the VENUS web site.
Tides and Ocean Mixing
The coastal waters of BC are subject to complex tidal variations, which not only cause the sea-level to rise and fall, but induce strong flood and ebb currents. Between islands, within channels and passages, these tidal currents are some of the most vigorous in the world, and churn the typically stratified ocean into a turbulent maelstrom. In conjunction with the estuarine circulation, tidal mixing disperses the fresh upper layer downward, and entrains the deep salty water upwards. Fortnightly variations in the tides modulate the mixing processes and dictate the strength and timing of deep water renewal and exchange flows. VENUS will directly measure the tidal currents and sea-level elevations in the southern Strait of Georgia, and using advanced acoustic Doppler current profilers (ADCP), provide real-time measurements of shear and ocean mixing events.
Understanding and managing our fisheries resources requires intimate knowledge of where and when species migrate and how they utilize specific habitats. Historically, the only way to know where and how many fish are in an area is to catch them. New technologies, however, allow us to tag juveniles with tiny acoustic beacons that periodically send out faint identifying chirps. Strategically placed receivers on the VENUS network will be able to monitor fish movement, residency times, and the timing of departure and return to a region. Goals including understanding local migratory habits, dependencies on regional ocean conditions, and mortality rates. Prime candidates for acoustic tagging are salmon and rock fish.
Delta Slope Stability
The Fraser River has a huge impact on the regional ocean conditions in the Strait of Georgia. This is particularly true at the mouth of the river, where fast-flowing sediment laden river water meets calmer seawater. Through a combination of reduced dynamics and coagulation, sediments rapidly settle within a few kilometres of the river mouth, forming the Fraser Delta. At the mouth, the bottom contours drop off steeply into the basin. This Delta slope is now compacted, and itself is a dynamic geological structure. Understanding slope stability and slope failure are key components of the VENUS network which will maintain a dedicated suite of specialized instruments near Sand Heads to monitor and study slope processes. Sensors will include piezometers, pore-pressure sensors, high-frequency sonar, acoustic Doppler current profiles near and above the bottom, and precision sea-level pressure gauges.
Sediment Transport and Bedform Dynamics
In addition to catastrophic slope failure events, the Delta Dynamics Laboratory of VENUS will study and monitor the sediment water boundary along the Delta slope. Monitoring the rate of sediment accretion, re-suspension, sediment transport, and bedform evolution will be accomplished using active, narrow-beam sonar and camera imagery.
Acoustic Monitoring of Air-Sea Interactions
The VENUS hydrophone array, in addition to monitoring marine mammals and anthropogenic noise, will detect and permit studies of natural sound generation mechanisms associated with air-sea interactions. Processes such as wind, rain, hail, wave breaking, and even lightening introduce significant ambient sound into the ocean. Tracking and analyzing the acoustic signals at the ocean bottom using the VENUS broadband hydrophones will be an active research project.
BC’s coastal ocean supports a diverse and vibrant suite of benthic ecosystems supporting a wide variety of organisms and important marine habitats. Most scientists study seafloor animals by dredging or occasional visits from submersibles. We know little about how the bottom habitat of Strait of Georgia is controlled by the swift, reversing tidal currents, sediment dumps from the Fraser, or overlying plankton blooms. VENUS is a unique opportunity to examine the adaptations of organisms to high flows. The facility may also give us those rare glimpses of large deep water animals. Scientists also plan studies of bottom community responses to large food falls such as carcasses.
- Richard E. Thomson, “Oceanography of the BC Coast“