Inner-shelf circulation off the central Oregon Coast
Permanent citation URL:
http://hdl.handle.net/1957/5113
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| Title: | Inner-shelf circulation off the central Oregon Coast |
| Authors: | Kirincich, Anthony R. |
| Advisors: | Barth, John A. |
| Committee Members: | Menge, Bruce Levine, Murray Dever, Ed Nash, Jonathan Watson, Philip |
| Keywords: | Oregon inner shelf circulation inner shelf dynamics coastal upwelling Ekman transport across shelf exchange momentum balances eddy viscosity |
| LCSH Keywords: | Ocean circulation -- Oregon -- Pacific Coast Ocean currents -- Oregon -- Pacific Coast Continental shelf -- Oregon -- Pacific Coast |
| Issue Date: | 24-May-2007 |
| Abstract: | Inner-shelf circulation and mechanisms of across-shelf transport of water masses were examined using seven years of observations collected by the Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO) program, a long-term monitoring effort along the central Oregon coast. Since 1998, moored velocity and hydrographic measurements have been obtained during the summer upwelling season in water depths of 30, 15, or 8 m at 3-5 stations along a 75 km stretch of the Oregon shelf. These observations enabled a description of along-shelf variations and upwelling dynamics in an area of intermittent wind forcing but little buoyancy influences. While wind forcing and bathymetry were nearly spatially uniform in the inner-shelf, circulation was spatially variable due to an offshore submarine bank. Classic two-dimensional upwelling existed north of the bank, with bottom stress and acceleration balancing the wind stress in the depth-averaged along-shelf momentum equation. This balance failed onshore of the bank where the pressure gradient and nonlinear advection were needed to close the momentum balance. Driven by along-shelf wind forcing, across-shelf surface transport was 25% of the theoretical Ekman transport at 15 m water depth, 1-2 km offshore, and reached full Ekman transport 5-6 km offshore in 50 m of water. This result, based on season-long comparisons of measured across-shelf transport and theoretical Ekman transport, defines the across-shelf scale of coastal upwelling on the Oregon shelf. However, observations of across-shelf circulation also highlight the rapid movement of water masses and variable residence times in the inner shelf. To quantify the time variability of across-shelf exchange, a numerical model was adapted to estimate vertical eddy viscosity using the velocity measurements. Resulting depth-averaged eddy viscosities ranged from 0.8x10[superscript −3] m [superscript 2] s[superscript −1] during upwelling winds to 2.1x8x10[superscript −3] m [superscript 2] s[superscript −1] during downwelling winds, consistent with previous numerical model results. The difference in eddy viscosities between upwelling and downwelling led to varying across-shelf exchange efficiencies and increased net upwelling over time. These results quantify the structure and variability of circulation in the inner-shelf and have significant implications for ecological processes (e.g., larval recruitment, nutrient availability) in the region. |
| Description: | Graduation date: 2007 |
| URI: | http://hdl.handle.net/1957/5113 |
| Appears in Collections: | Physical Oceanography Theses, Dissertations and Student Research Papers (COAS) Electronic Theses and Dissertations |
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