http://hdl.handle.net/1957/1311 Search the Channel search http://ir.library.oregonstate.edu/jspui/simple-search http://hdl.handle.net/1957/8328 Title: Variability in mesoscale circulation and its effects on zooplankton distribution in the Northern California Current<br/><br/>Authors: Keister, Julie Eileen<br/><br/>Abstract: In eastern boundary current upwelling ecosystems, mesoscale circulation features such as eddies and upwelling filaments play a prominent role in the transfer of water and the associated plankton from the productive nearshore to the oligotrophic deep sea. The relationship between mesoscale circulation, zooplankton distributions, and the across-shelf transport of coastal taxa and biomass in the California Current System was studied using data collected as part of the U.S. Global Ocean Ecosystems Dynamics (GLOBEC) Northeast Pacific Program. Sea surface height from >13 years of satellite altimeter data was used to characterize the spatial and temporal variability in mesoscale circulation in the northern California Current (35°N-49°N) and explore mechanisms of variability. High spatial and temporal variation in mesoscale energy occurred. Energy was not strongly linked to upwelling winds, but did correspond to climate indices, indicating that basin-scale processes play a role in controlling the circulation. CTD casts, zooplankton net tows, and Acoustic Doppler Current Profiler (ADCP) velocities collected during a research cruise conducted in summer 2000 off Oregon and northern California were used to describe the effects of mesoscale circulation on distributions of zooplankton. During the cruise, a filament of the coastal upwelling jet extended seaward of Cape Blanco (42.8°N) resulting in the displacement of coastal zooplankton to >100 km off the continental shelf. Velocities and standing stocks of zooplankton were used to estimate seaward transport of 0.5 Sv in the upper 100 m of the filament, in which zooplankton biomass averaged ~20 mg carbon/m³. That offshore transport equated to >900 metric tons of carbon each day, and 4-5x10⁴ tons over the 6-8 week lifetime of the circulation feature. Although the flux represented a small portion (<2%) of the shelf zooplankton biomass, the transport resulted in an offshore "hot-spot" in which biomass was 3-4X higher than in the surrounding ocean. Distributions of early life history stages of euphausiids indicated that retention of coastal populations may be strongly affected by the offshore advection. Finally, satellite sea surface temperature (SST) and sampling conducted during five summers were used to explore variability in the relationship between mesoscale circulation features and distributions of zooplankton. Circulation patterns differed among cruises and were reflected in zooplankton distributions. Circulation features resulted in the occurrence of cold surface water and coastal taxa offshore, but species abundances and presence/absence of taxa at specific locations were not predictable from satellite SSTs. These results are relevant to studies of ecosystem dynamics and the global carbon cycle because mesoscale circulation plays an important role in the seaward transport of carbon, retention and loss of taxa from the continental shelf, and creation of offshore structure which may be exploited by upper trophic level organisms.<br/><br/>Description: Graduation date: 2008 Tue, 15 Apr 2008 22:52:02 GMT http://hdl.handle.net/1957/7448 Title: Characterizing the habitat and diving behavior of satellite-tagged blue whales (Balaenoptera musculus) off California<br/><br/>Authors: Irvine, Ladd<br/><br/>Abstract: This study was designed to identify and characterize areas of concentrated use and diving behavior of blue whales (Balaenoptera musculus) off the California coast. During the summer of 2004, thirteen blue whales were tagged with implantable Telonics ST-15 Argos satellite-monitored radio tags and five were tagged with Telonics ST-21 Argos satellite-monitored depth of dive tags. Tag duration averaged 100 d with a total of 2159 locations recorded. Whales generally remained near the continental slope and were most often found at the west end of the Santa Barbara Channel, near the Gulf of the Farallones, or between Cape Mendocino and Cape Blanco. Analysis of the 95% kernel density distributions of whale locations showed a one degree increase in sea surface temperature (SST) was correlated with a decrease in whale density by 7% (p < 0.0001) while density was highest at a surface chlorophyll level of 4.5 mg/l and a water depth of 1573 m (p < 0.001 each). These results show that tagged whales were most likely to be found in areas of strong upwelling along the slope edge. Dive data from 414 summary periods showed whales spent at least 50% of their time in the top 50 m of the water column and up to 94% of their time there at night. Daytime average dive depth was 2.3 times deeper than during the night, probably due to the vertical migration of some euphausiid species upon which blue whales feed. Differences in mean number of dives and mean maximum dive duration suggest a behavior change during the night, possibly a period of rest. Whales dove less frequently as swim speed increased, and more frequently as water depth increased. No significant variation in daytime average dive depth was observed between clustered and linear location types, however fewer total dives were made during linear location types suggesting whales were making exploratory dives to foraging depths while traveling.<br/><br/>Description: Graduation date: 2008 Mon, 31 Dec 2007 23:31:42 GMT http://hdl.handle.net/1957/3191 Title: Phosphorus physiology and environmental forcing of oceanic cyanobacteria, primarily Trichodesmium spp.<br/><br/>Authors: White, Angelicque E.<br/><br/>Abstract: The biological transformation of dinitrogen gas (N2) into combined forms(termed N2 fixation) by certain genera of oceanic cyanobacteria represents the largest incoming flux of nitrogen to the global ocean. As such, biological nitrogen fixationplays a significant role in the regulation of oceanic productivity and the export ofcarbon and nitrogen out of the sun-lit surface waters. Currently, our knowledge of the biogeochemical and ecological significance of N2-fixing organisms is restricted by our relative inability to define mechanistically the relevant chemical, biological and physical controls of the production and abundance of biological N2 fixation in the marine environment. The four chapters that form the main body of this dissertation touch upon specific aspects of the controls of the production and abundance of N2-fixing organisms, particularly that of the cyanobacterial genus Trichodesmium.Chapter II defines the range of intracellular elemental composition exhibited by Trichodesmium and identifies phosphorus (P) as a key factor limiting N2 fixation by populations of this organism residing in specific regions of the Atlantic and Pacific oceans. Chapter III explores vertical migration as a physiological adaptation relevant to the growth of this same cyanobacterium, Trichodesmium. Results from this work indicate that vertical migration may allow a subset of the population to exploit the separation of light and nutrients under stratified oligotrophic conditions, thus potentially supplementing their P requirements for growth. Chapter IV examines time-seriesrecords in an attempt to define the physical characteristics of the environment that may regulate surface blooms of cyanobacteria. These analyses indicate that season, sea surface temperature and mixed layer depth are the most constrained predictors of blooms of N2-fixing cyanobacteria in the North Pacific. Lastly, Chapter V identifies a novel region of the ocean inhabited by N2-fixing organisms.<br/><br/>Description: Graduation date: 2007 Mon, 23 Oct 2006 17:36:13 GMT http://hdl.handle.net/1957/2852 Title: Impact of tropical instability waves on nutrient and chlorophyll distributions in the equatorial Pacific<br/><br/>Authors: Evans, William Wiley<br/><br/>Abstract: Tropical instability waves (TIWs) are prominent seasonal features in both the equatorial Pacific and Atlantic Oceans. This work quantifies their role in modulating the distributions of nutrients and phytoplankton biomass. Using an eight year record of biannual ship observations along the Tropical Atmosphere Ocean (TAO) buoy array, cruise sections crossing TIWs were identified. Both a case study approach of individual TIWs and a first attempt at calculating their average effect on mixed layer properties were performed. Examination of individual TIWs demonstrates that their effect on nutrient and chlorophyll distributions is a function of the TIW intensity. Both strong and weak TIWs drive elevated nutrient concentrations directly on the equator, but strong TIWs possess enhanced recirculation which advects nutrient- and chlorophyll-poor waters from adjacent to the upwelling zone equatorward. This decreases nutrient concentrations from approximately 2°N to 8°N. Weak TIWs retain elevated nutrient concentrations in this latitudinal band due to less recirculation in TIW vortices, permitting chlorophyll increases. These differences between strong and weak TIWs were only observed north of the equator. Less recirculation was observed in TIW vortices south of the equator. This resulted in nutrient enhancements from TIWs along the southern portions of the cruise sections, especially in the eastern Pacific. The differences between northern and southern TIW dynamics suggest strong differences in TIW modulated carbon cycling between the two hemispheres. Seasonal modification of the equatorial currents also influences the extent to which TIWs alter nutrient and chlorophyll distributions. TIWs observed during boreal winter demonstrated enhanced nutrient and chlorophyll concentrations north of the equator. This resulted from the water mass north of the upwelling zone containing elevated nutrient and chlorophyll concentrations due to a shallow thermocline. Thermocline shoaling in boreal winter is the result of a slowing in the South Equatorial Current and North Equatorial Countercurrent caused by the seasonal decrease in westward trade wind velocities. These results suggest that there is a synergistic effect from TIWs and the seasonal shoaling of the thermocline which may be important for carbon cycling north of the equator.Composites of average mixed layer nutrient concentrations show TIW-induced nutrient enhancement on and south of the equator along most of the TAO lines, but no subsequent increase in mixed layer chlorophyll. This is likely due to the lag time between nutrient enhancement and biomass increase and/or chlorophyll increases in unsampled portions of the vortex. Regions of elevated chlorophyll concentrations were observed in SeaWiFS composites in unsampled portions of TIWs, which suggests that TIW induced lateral transport of nutrients may be driving important episodic export events south of the equator.<br/><br/>Description: Graduation date: 2007 Mon, 07 Aug 2006 20:17:00 GMT