Graduate Thesis Or Dissertation
 

Diurnal wind-driven processes on the northern Monterey Bay inner shelf

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/qz20sv905

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  • In the summer of 2007, a biophysical experiment was conducted to identify physical processes that determine the delivery of invertebrate larvae and juvenile rockfish to rocky intertidal and kelp forest communities in northern Monterey Bay, California. The experiment was sponsored by the Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO) and collected physical measurements including velocity from acoustic Doppler current profilers, surface gravity wave heights measured acoustically, and temperature from thermistor chain arrays both along- and across- the inner shelf in water depths of 10 – 60 m. The inner shelf is the transition between the nearshore and mid-shelf zones, and is defined where surface and bottom Ekman boundary layers overlap. Previous work has shown that the inner shelf in this region is rich in physical processes across many space and time scales. The goal here is to identify and quantify the dominant processes at the diurnal (24 hour) period. Diurnal tides contribute less than 10% of the observed currents. Thus the focus is on the oceanic response to a strong (8 - 15 m/s daily maximum) along-shelf sea breeze which forces offshore surface Ekman transport, drives average upwelling velocities of 26 m/day, and cools the water column 2 – 4 degrees/day. At 15 m (20 m) depth, measured diurnal surface transport is 36% ± 9% (77% ± 12%) of full theoretical Ekman transport. Examination of a diurnal heat budget shows that vertical advection is the dominant process during afternoon cooling (both horizontal advection and solar insolation are sources of heat during this period), and is needed to close the heat budget to within 5%. In contrast, during evening/early morning heating 92% of the observed heating is explained by along-shelf advection of a temperature gradient within the upwelling shadow, much greater than the heating attributed to either solar insolation (2%) or onshore motions (2%). Thus, the diurnal heat budget is closed to within a few percent and explained by two-dimensional processes: vertical advection by wind-driven upwelling during cooling and along-shelf advection during heating.
  • Keywords: Inner shelf, Monterey Bay, coastal, wind-driven, physical oceanography
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