Svein Helge Gjøsund

Engineered and Natural Marine Seep, Bubble-Driven Buoyancy Flows

Abstract Bubble-plume upwelling flows were studied in the marine environment through dye releases into engineered plumes and a natural hydrocarbon seep plume. For engineered plumes, these experiments measured the water column–averaged upwelling flow Vup(zo) from release depth zo to the sea surface, for a wide range of flows Q, and zo. From Vup(zo), the local upwelling flow Vup(z), where z is depth, was calculated and found to vary with Q as Vup(z) ∼ Q0.23 for plumes strong enough to penetrate a shallow, thermally stratified layer, which was in good agreement with published relationships between Vup(z) and Q. These data were used to interpret data collected at a natural marine seep. For the seep, the upwelling flow decelerated toward the sea surface in contrast to the engineered plumes, which accelerated toward the sea surface. Data showed the seep bubble-plume upwelling flow lifted significantly colder and more saline water. The increased density difference between this upwelling fluid and the surrounding...

Pneumatic oil barriers: The promise of area bubble plumes

Reviews of bubble curtain oil herding studies in 1971 and in 1997 concluded that a bubble oil boom, or pneumatic oil barrier, is ineffective for retaining oil spills except in quiescent water, such as harbors. A bubble oil boom generates a sea-surface outwelling flow that traps or blocks oil. The primary bubble oil boom failure mode arises from oil droplet injection due to turbulence and instabilities at the oil slick front, where the outwelling flow balances the oil spreading. Bubble oil boom leakage occurs where these droplets are entrained into and pass through the bubble barrier. Increasing bubble flow creates stronger outwelling flows but increases turbulence and instabilities, leading to enhanced oil droplet entrainment. Natural seep observations, field trials, and laboratory studies demonstrate that a bubble plume with a wide bubble oil boom area, which is driven by an array of several parallel spargers (a bubble raft), can increase oil retention greatly while addressing key bubble oil boom failure modes compared with a line-source bubble curtain plume. Further improvements are identified by synergistic bubble oil boom application with a retaining skirt, dramatically improving the bubble oil boom performance. Specifically, the bubble oil boom keeps the oil distant from the skirt, minimizing or eliminating several conventional oil boom failure mechanisms. Also, entrained droplets, which easily traverse a single bubble curtain, are blocked effectively by a wide bubble plume curtain.

Commercial Exploitation of Zooplankton in the Norwegian Sea

Since 1990s there has been increased interest in the exploitation of marine zooplankton like copepods and krill. This has been motivated by the increasing demand for marine bioresources for human consumption in general, and in particular the growing demand for feed in aquaculture. In Nordic Seas, zooplankton is a key component in the energy transfer from primary producers to higher trophic levels such as herring, capelin, salmon, cod larvae and juveniles, and other species (Skjoldal, 2005). Roughly 70-80% of the zooplankton production in these waters is made up by copepods of the genus Calanus (Tande and Miller, 2000). According to general ecological theory about 10% of this production is available to the next trophic level (Lalli and Parsons, 1997). Estimates of the total annual production of Calanus sp. vary between 75 million tons y−1 for the Nordic Seas (Aksnes and Blindheim 1996) and 300 million tons Calanus sp. (mainly Calanus finmarchicus) y−1 for the Norwegian Sea only (Skjoldal et al. 2004).