I used a specific inhibitor approach to systematically measure NH4+ oxidation rates through the euphotic zone of three distinct oceanographic regimes. Study sites included Saanich Inlet, a highly productive British Columbia fjord, the Line P oceanographic transect in the NE subarctic pacific, and the Bermuda Atlantic Time-series Study (BATS) station in the oligotrophic, sub-tropical Sargasso Sea. Nitrate uptake rates were also measured at select stations on a number of research cruises. NH4+ oxidation rates were found to proceed throughout the euphotic zone in each of my study regions, and, overall, euphotic zone NH4+ oxidation rates ranged from undetectable to 203 nmol L-1 d-1. A general characterization of the rates observed in each of my study regions shows that euphotic zone NH4+ oxidation rates were typically highest in Saanich Inlet, intermediate along Line P, and lowest at BATS. The observation that NH4+ oxidation occurred throughout the euphotic zone in each of my study regions was in contrast to the traditional assumption of no euphotic zone nitrification, and it should now be considered a ubiquitous process in the euphotic regions of the ocean. Results found that euphotic zone nitrification could have potentially supported, on average, 15, 53 and 79% of the phytoplankton NO3- requirements in Saanich Inlet, and along Line P and at BATS, respectively, and this underscores the need for a major re-evaluation of the new production paradigm. Light, substrate concentrations, and potentially substrate supply rates were all found to play a role in regulating NH4+ oxidation, albeit to varying degrees, and I discuss the influence that each of these variables may have had on controlling NH4+ oxidation rates at regionally specific scales in Chapters 2 (Saanich Inlet), 3 (Line P) and 4 (BATS). Finally, a cross study-region comparison of results showed that the relative degree by which new production estimates were reduced, when euphotic zone nitrification was taken into consideration, decreased exponentially as total NO3- uptake rates increased; the relationship I describe between these two variables may potentially provide a simple and rapid means of estimating the extent to which new production may have been overestimated at regionally specific and global scales. My Line P sampling program also provided me with an opportunity to conduct the first investigation of intermediate depth N2O distributions along the Line P oceanographic transect. My results demonstrated that nitrification is the predominant production pathway for N2O in the NE subarctic Pacific. N2O distributions along Line P were variable, however, and I also consider the role of different transiting water masses and potential far-field denitrification in contributing to this variability. Finally, I estimated sea-to-air fluxes of N2O and based on these results I have demonstrated that the NE subarctic Pacific is a “hotspot” for N2O emissions to the atmosphere. / Graduate

In Saanich Inlet, a fjord located in southern Vancouver Island, British Columbia, dense aggregations of euphausiids exhibit diel vertical migration behavior and their capability of generating turbulence has been suggested. Despite decades of research on diel vertical migration of zooplankton, its variability has not been well studied. In addition, the physical oceanographic environment in Saanich Inlet has not been thoroughly quantified, which raises the possibility of previously observed turbulent bursts of O(10^-5 – 10^-4 W kg^-1) having physical (rather than biological) origin. This work characterizes variability of diel vertical migration behavior using a moored 200-kHz echosounder, complemented by plankton sampling. Physical properties such as barotropic, baroclinic and turbulent signals are described, and the relationship between turbulence and internal waves/scattering layer examined. A two-year high-resolution biacoustic time-series provided by the Victoria Experimental Network Under the Sea (VENUS) cabled observatory allowed quantification of the seasonal variability in migration timing of euphausiids. During spring – fall, early dusk ascent and late dawn descent relative to civil twilight occur. During winter, late dusk ascent and early dawn descent occur. Factors regulating the seasonal changes in migration timing are light availability at the daytime depth of the scattering layers, and size-dependent visual predation risk of euphausiids. Instead of the traditional view of diel vertical migration timing correlated solely with civil twilight, euphausiids also adapt their migration timing to accommodate changes in environmental cues as well as their growth. The pre-spawning period (February – April) is an exception to this seasonal pattern, likely due to the higher energy demands for reproduction. Turbulence and internal waves in Saanich Inlet are characterized based on a one-month mooring deployment. Average dissipation rates are nearly an order of magnitude larger than previously reported values and higher dissipation rates of O(10^-7 – 10^-6 W kg^-1) are occasionally observed. A weak correlation is observed between turbulent dissipation rates and baroclinic velocity/shear. To examine the possibility of biological generation of turbulence, an echosounder at the VENUS cabled observatory is used to simultaneously measure the intensity of the euphausiid scattering layer and its vertical position. Turbulent bursts of the sort previously reported are not observed, and no relation between diel vertical migration and turbulent dissipation rates is found. Physical forcing at the main channel remains as a possible cause of the turbulent bursts. / Graduate / 0416 / 0415

The present study investigated the temporal and spatial dynamics of primary productivity, total and size-fractionated chlorophyll a, phytoplankton taxonomic composition, dissolved nutrients, and temperature and salinity in the euphotic zone of Saanich Inlet. Seawater sampling was carried out monthly from May 2005 to November 2006 at the mouth and head of Saanich Inlet. Physical and chemical data indicated that spring/neap tidal cycles supplied nutrients to the head as well as to the mouth region of Saanich Inlet. Of the three nutrients (N03-, Si(OH)4 and P043) measured, N03- was identified as the potentially limiting nutrient for phytoplankton growth. During the growing season, three major phytoplankton bloom periods were observed in Saanich Inlet: a spring. a summer and a fall bloom, and phytoplankton assemblages were consistently dominated by micro-phytoplankton (mainly diatoms). During both the 2005 and 2006 growing season, rates of primary production and phytoplankton biomass were highest during the summer blooms, and results suggest that these blooms were triggered by peak freshwater discharge from the Fraser River. The estimated annual rate of total primary production in Saanich Inlet was 461 g C m-2 year-l. On average primary productivity was 1.5 times higher at the mouth than at the head of Saanich Inlet during the growing season. Results indicated that this difference was caused by a combination of lower NO3- concentrations and lower micro-phytoplankton biomass at the head of Saanich Inlet in comparison to the mouth. Throughout the 2005 and 2006 growing season, micro-phytoplankton contributed significantly to primary productivity in Saanich Inlet, indicating that a substantial portion of primary production was based on new primary productivity. This was confirmed by measurements of new primary production from May to October 2006. During this period, new primary production was responsible for 53 and 57% of total primary production at the head and mouth of Saanich Inlet, respectively. The results reported in this study have significantly improved our understanding of the factors that control the temporal and spatial variability of primary productivity in Saanich Inlet.

Pollen records from southeastern Vancouver Island, British Columbia, show changes in vegetation and climate from the late Olympia Interstade through the Fraser Glaciation. This study provides important insights into phytogeographic patterns of Pacific Northwest flora, leads to an enhanced understanding of processes affecting present-day ranges of several plant taxa, and provides a historical perspective on the origin of coastal alpine ecosystems. Evidence for a previously unrecognized glacial advance in the region at ~21,000 14C yr BP, herein called the Saanich glacier, is provided. The results reveal widespread habitat and food sources suitable for the mega fauna that lived on southern Vancouver Island during the last glaciation. Vegetation during the Fraser Glaciation represented a mosaic of plant communities across a heterogeneous and productive landscape. Pollen spectra indicate that plant assemblages, dominated by Poaceae and Cyperaceae, were widespread. Similarities to tundra in northern Alaska and high elevation sites in British Columbia were detected. Vegetation varied geographically in the late Olympia (ca. 33,500-29,000 14C yr BP). Grassy uplands with scattered trees and local moist meadows occurred at Qualicum Beach under mesic and cool conditions, while cold and dry grass tundra prevailed at Skutz Falls. Increased non-arboreal pollen percentages at Qualicum Beach, 29,000 14C yr BP, reflect expansion of grassy meadows with diverse herbs under a cool and dry climate at the onset of the Fraser Glaciation. At Qualicum Beach between 25,160-24,190 14C yr BP, sedge wetlands were surrounded by open, dry uplands. Concurrently at Osborne Bay, Pinus-Picea-Abies-Poaceae parkland occurred. Dry and cold climate intensified as the Fraser Glaciation progressed after 24,000 14C yr BP and non-arboreal communities expanded. At Cordova Bay, cold and dry tundra or parkland in upland sites, and sedge wetlands on an aggrading floodplain are recorded. Sparse tree cover and grass-tundra surrounded a floodplain at Skutz Falls around 21,000 14C yr BP under cool and dry climate. Subalpine-like Picea-Abies-Pinus parkland and moist, species-rich grassland meadows occurred at McKenzie Bight at the same time. A sedge wetland occupied the site of deposition, and was periodically inundated as lake levels fluctuated. Upland grasslands at Cordova Bay are recorded between 21,600–19,400 14C yr BP, while local ponded areas developed on an aggrading floodplain at sea level. From 19,400-19,300 14C yr BP, parkland at Cordova Bay developed as climate moistened and warmed at the time of the Port Moody Interstade known from the Fraser Lowland. Abundant marine dinoflagellate cysts between 21,600–19,400 14C yr BP, reveal a high sea level stand and strong marine influence at Cordova Bay. Glacioisostatic depression of the crust on the east side of Vancouver Island is the most probable explanation. The presence of pollen-bearing glacio-lacustrine sediments at McKenzie Bight around 21,000 14C yr BP at ~93 m and contemporaneous isostatic crustal depression at Cordova Bay strongly suggest a major glacial body in the region at the same time as the Coquitlam advance in the Lower Mainland. Ice-free landscapes may have occurred on southern Vancouver Island through the Fraser glaciation beyond the Saanich glacier ice limits. / Graduate