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.

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

Le système du Courant de Californie (CCS) est l'un des grands systèmes d'upwelling de bord est de la planète, caractérisés par un régime saisonnier de vents qui provoque des remontées d'eaux profondes (upwelling côtier), riches en nutriments, favorisant une forte activité biologique. À long terme, l'écosystème du CCS révèle des alternances de dominance de communautés marines, encore inexpliquées. L'objet de cette thèse est de comprendre l'effet de la variabilité pluriannuelle des vents sur la structure et le fonctionnement des premiers maillons trophiques de l'écosystème du CCS à partir d'études de processus reposant sur une approche numérique. Une première étude a permis de montrer que l'upwelling côtier et le transport côte-large ont une variabilité à basse fréquence fortement corrélée à celle de la tension de vent parallèle à la côte et au mode North Pacific Gyre Oscillation (NPGO), mis en évidence récemment et connu pour capturer une part de la variabilité à basse fréquence des vents d'upwelling et de la chlorophylle dans le CCS. Une étude fine de ces vents a permis de mettre en évidence une relation forte entre leur variabilité saisonnière et le mode NPGO, avec une modulation temporelle du déclenchement de la saison d'upwelling du CCS. L'impact d'un tel déphasage de l'upwelling sur un écosystème planctonique a pu ensuite être testé. À la côte, l'écosystème répond directement à un scénario d'upwelling précoce par une productivité plus forte. Au large, les incidences sur l'écosystème s'opèrent via les processus de transport côte-large. L'effet sur le zooplancton est plus prononcé que sur le phytoplancton et est susceptible d'affecter les niveaux trophiques supérieurs.