Thesis (M.S.)--Naval Postgraduate School, 1975. / Includes bibliographical references (leaves 105-106).

Thesis (M.S.)--Naval Postgraduate Schoool, 1990. / "September 1990." Includes bibliographical references (p. 142-146).

Thesis (M.S.)--Naval Postgraduate School, 1975. / Includes bibliographical references (leaf 140).

Thesis (M.S.)--Naval Postgraduate School, 1984. / Includes bibliographical references (p. 143-145).

Thesis (Ph. D.)--University of California, San Diego, 2000. / Vita. Includes bibliographical references.

Chrysaora fuscescens is a cnidarian scyphomedusa that occurs in the northern California Current. In this upwelling system, medusae are seasonally abundant, and individuals can ingest 10-60% of the standing stock of vulnerable zooplankton taxa per day. Yet little is known about this medusa's feeding ecology. Using laboratory pseudokreisels, C. fuscescens feeding rates and behavior were quantified in the presence of a controlled flow field. C. fuscescens collected aboard research cruises were dissected, and prey items were counted in order to calculate feeding rates and prey selectivity. In the lab, C. fuscescens feeding rates were not affected by shear flow, and medusa maintained position by swimming counter-current. Field work demonstrates high feeding rates and positive prey selection for nonmotile taxa. For the first time, high clearance rates of ichthyoplankton have been documented. An understanding of jellyfish behavior can help explain jellyfish distributions and trophic impacts in a productive upwelling system.

The California Current system (CCS) is home to a vast and diverse marine coastal ecosystem. Upwelling is an oceanic phenomenon wind-driven displacement of surface water brings cold nutrient-rich water from the ocean bottom to surface waters. Along the coast in the CCS, upwelling occurs via the advection of water perpendicular to the shoreline northerly winds, a phenomenon called “Ekman Transport”. In the open ocean. Wind stress curl causes disruption of normal currents, resulting in small pockets of upwelled or downwelled water (downwelling is the movement of water downward in the ocean, the opposite of upwelling). This process is called “Ekman Pumping”, and over large swaths of ocean, it can result in a notable increase/decrease in net upwelling. Upwelling is one of the main driving forces behind the diversity and strength of the ecosystems within the CCS. The Bakun hypothesis (Bakun, 1990) suggests that with the future increase of atmospheric greenhouse gases (GHGs), Eastern Boundary Upwelling Systems (EBUSs) will experience an increase in upwelling intensity and season duration. The Bakun hypothesis has been proven to be an accurate description of the mechanisms of change expected in all major EBUSs in the world, except for the CCS, where only weak correlations have been made (Sydeman, García-Reyes, Schoeman, D. S. Rykaczewski, R. R. . Thompson, Black, & Bograd, 2014). A recent study by Wang et al. 2015 found weak correlations of decreases in upwelling intensity in the CCS, which would suggest that the Bakun Hypothesis does not accurately depict the future of the CCS. Previous climate change CCS studies have relied on atmosphere-ocean global climate models (AOGCMs), which are typically performed on a horizontal grid too coarse to accurately depict the physical changes expected in the CCS. In this study, a 10-member ensemble of high resolution regional climate model (RCM) climate change experiments driven by 10 AOGCMs is used to project changes in the timing and intensity of the upwelling season within the CCS and test the Bakun Hypothesis. We also consider Surface Temperature to extrapolate how changes, if any, compound or counteract the accuracy of the Bakun Hypothesis. We find a significant decrease of 6 m^3/s/100m in mean Ekman Transport and an increase of 1.3 ⁰C in mean Surface Temperature. A 1.1×10^(-06) m/s decrease in mean Ekman Pumping is also observed, but these findings are not robust. We also find no change to the length or timing of the upwelling season. The decrease in Ekman Transport and increase in Surface Temperature could compound upon each other and cause damage to vulnerable ecosystems within the CCS, most notably in the latitudinal range of 34°-40° along the coast, as future GHGs concentrate in the atmosphere. In the shallow ocean, decreased upwelling intensity and increased stratification will inhibit the movement of nutrients that primary producers rely on, thus stifling phytoplankton and zooplankton growth. Increases in surface temperature could also create new avenues of environmental stress that local communities are not prepared to adapt to, resulting in decreased physiological performance and potentially geographical shifts in species residence. These changes to shallow ocean communities could have cascading effects on the availability of prey up the trophic web. In the deeper ocean, decreased upwelling intensity and increased stratification will inhibit ocean mixing, and thus decrease availability of dissolved oxygen in the deeper ocean. This could result in hypoxic and anoxic events and create major species die-off in local communities.

Variable ocean conditions can greatly impact lower trophic level prey assemblages in marine ecosystems, with effects propagating up to higher trophic levels. Our goal was to better understand how varying ocean conditions influence diets and niche overlap among a suite of low- to mid trophic level predators. We studied the diets of common murres (Uria aalge) over 10 contrasting years between 1998 and 2011, a period in which the Northern California Current experienced dramatic interannual variability in ocean conditions. Likewise, murre diets off Oregon varied considerably. Interannual variation in murre chick diets appears to be influenced by environmental drivers occurring before and during the breeding season, at both basin and local spatial scales. While clupeids were an important diet component throughout the study period, in some years murre diets were dominated by Pacific sand lance (Ammodytes hexapterus) and other years by osmerids (likely Allosmerus elongatus and Hypomesus pretiosus). Years in which the Pacific Decadal Oscillation and local sea surface temperatures were above average during summer months also showed elevated levels of clupeids in murre diets, while years with higher winter ichthyoplankton biomass and summer northern copepod biomass anomalies had fewer clupeids and more sand lance and smelts. Years with higher Northern Oscillation Index values during summer months also showed more smelts in the murre diets. Nesting phenology and reproductive success were correlated with diet as well, reflecting demographic consequences of environmental variability mediated through bottom-up food web dynamics. To examine niche overlap between murres and other marine predators we employed collaborative fisheries research with synoptic observations of a major seabird colony to determine the diets of four predator species on the central Oregon coast during two years of contrasting El Niño (2010) vs. La Niña (2011) conditions. The greatest degree of dietary overlap was observed between Chinook salmon (Oncorhynchus tshawytscha) and common murres, with both smelts (Osmeridae) and clupeids (primarily Clupea pallasii) observed as the dominant prey types. Diets differed between El Niño and La Niña conditions for two predators, murres and black rockfish (Sebastes melanops). During La Niña, smelts decreased, while sand lance increased in common murre diets. Black rockfish had fewer larval Dungeness crabs (Cancer magister) and a greater proportion of crab species associated with the later spring transition. Chinook salmon and Pacific halibut (Hippoglossus stenolepis) diets were similar during El Niño and La Niña conditions. These findings underscore that the diets of common murres during chick rearing reflect local- and basin-scale biophysical processes in the Northern California Current, and are valuable for understanding the response of upper trophic level organisms to changing oceanographic conditions. Additionally, using multiple predators across several diverse taxa to track changes in prey communities provided a way to detect seemingly subtle changes in prey communities and contributes to a more comprehensive understanding of food web dynamics and ecosystem indicators. / Graduation date: 2012

Approved for public release; distribution in unlimited. / Moored current meters were used to describe currents over the continental slope off Monterey Bay, California, from March 1998 to March 2003. The water depth at this location was 1800 m and current observations included of 16-88 m, 210- 290 m, 305 m and 1200 m although measurements at 16-88 m were not continuous. Poleward currents dominated the flow between 24 and 305 m. At 305 m the mean flow was 3.9 cm/s toward 334ʻ. Surprisingly, at 1200 m the mean flow reversed and was 0.8 cm/s toward 169ʻ. The principal axis for the flow at 305 m (1200 m) was 349ʻ (350ʻ), the semi-major axis was 9.4 cm/s (5.8 cm/s) and the semi-minor axis 3.4 (2.0 cm/s). The direction of the principal axis and the mean flow at 1200 m was aligned with the bathymetry to the east of the mooring site. The seasonal cycle at 305 m was dominated by an acceleration of the poleward flow from a minimum near zero on April 15 to maximum, 25 cm/s on July 15. This flow resulted in an increase of temperature at 305 m of 1.2ʻC due to geostrophic adjustment and a corresponding 10 cm increase in sea level due to steric effects. The acceleration of alongshore flow was out of phase with the alongshore pressure gradient which was greatest in mid- April. At 1200 m, the temperature increase (0.2ʻC) only lasted from April 15 to June 1 after which equatorward flow increased and temperature decreased. Mesoscale variability dominated the velocity measurements with maximum variance at about 60- day periods. At 305 m, the eddy kinetic energy was greatest (smallest) in October (December), 40 cm2/s2 (4 cm2/s2) while at 1200 m the maximum (minimum) occurred in July (February), 5 cm2/s2 (0.5 cm2/s2). Poleward events were stronger at 305 m while equatorward events were stronger at 1200 m. The three first empirical orthogonal functions explained 90% of the temporal variability of the horizontal currents. The first, second, and third Z-scores represented flow along the principal axis, undercurrent vs. Davidson current, and upwelling modes, respectively. While the seasonal patterns for the first two modes agreed with seasonal variability described above, the seasonal variability of the upwelling mode (6% of the variance) indicated that the waters between 16 and 88 m flowed onshore during the spring and summer upwelling period. / Commander, Mexican Navy

Approved for public release, distribution is unlimited / During the fall of 2002 the physical oceanographic conditions off Central California were monitored by means of CTD casts and VMADCP current measurements during two cruises. The first cruise, included 38 stations and one time series station. The second cruise was sponsored by the Naval Oceanographic Office (NAVOCEANOCEANO) and occupied nine sections along the coast. A total of 86 stations and two time series stations were occupied during the second cruise. CTD calibration and data processing methods are described. The isosteres, current vectors, and salinity distribution from the cruises provide a clear picture of the circulation pattern during the fall 2002. A strong shoreward, anticyclonic meander of the California current was observed. Although the meander itself did not cross the dynamic trough that separated inshore and offshore currents, at the point where the meander was adjacent to the trough, a ridge formed which transported Subarctic waters into the coastal zone. These fresh waters were advected to the north and south along the coast, depending upon the direction of nearshore currents. The observed mesoscale circulation showed the manner in which waters which are upwelled at the coast in summer are replaced by oceanic waters in the fall and winter. Analysis of the geography of the deep sound channel (DSC) during this period showed that the mean pressure of the DSC was at 586 dbar while the mean sound speed minimum was 1480 m/s. The minimum sound speed varied 3 m/s while the pressure of the minimum varied by 330 dbars. The shape of the pycnocline controlled the pressure and depth of the DSC in the region. / Ensign, United States Naval Reserve