The upper ocean is host to overlapping vortical and internal waves dynamics over the submesoscales (10-100km), both of which are poorly represented in eddy-resolving ocean models. We analyze upper-ocean (0-200 m) horizontal-wavenumber spectra along Line P in the North Pacific subpolar gyre from shipboard ADCP measurements in February and June (2013-2015), and compare them to spectra from a 1/36th degree numerical simulation output. At scales between 10 and 100 km, the ADCP along-track (Cv) and across-track (Cv) kinetic energy spectra approximately follow power laws of k-2 and have a ratio R = Cv/Cu - 1. For purely non-divergent motions, the order of the power law and R should be the same, so divergent motions are evident. A Helmholtz decomposition estimates the fraction total kinetic energy that is contributed by internal-wave and vortex components. Vortex components follow a power law of k-2 with ratio R-2, consistent with predictions for a non-divergent flow, while internal waves are mostly consistent with the Garrett and Munk internal wave model. There are modest seasonal changes; vortical motions are slightly stronger in February than in June, whereas the amplitudes of the internal wave component increases in June. Depth variability of non-divergent vortical flows shows that at low wave-numbers energy decreases and that the kinetic energy spectra are bluer with depth, inconsistent with predictions from surface quasi-geostrophic theory of redder spectra with depth. Conversely, in the simulation the depth variability of the decomposed vortex components is in agreement with predictions of surface quasi-geostrophic theory. The simulations had very weak internal waves fields. / Graduate / 0415 / manmanw@uvic.ca

Primary production and carbon export connect biogeochemical cycles in the surface waters to the deep. Quantifying rates of production and carbon export are important to understanding the global carbon cycle. There are multiple productivity rate methods, but each measures a different fraction of production. The first type of method is in vitro methods that involve removing water samples from the environment and incubating with an isotopically labelled tracer, such as a nutrient. At the end of the incubation, the amount of enrichment in either the particulates (phytoplankton) or the dissolved oxygen are measured to determine productivity. The second type of method is in situ methods that measure the natural environmental parameters instead of incubations. In this study, the natural isotopic composition and the ratio of gases in the surface water are measured. Comparing in situ versus in vitro methods in the Arctic on a GEOTRACES cruise (July 2015), we identified five reasons to explain why methods do not agree: time of integration, depth of integration, recently shoaled mixed layer, mixing at the base of the mixed layer, and methodological issues. When comparing in vitro methods to each other, filter handling and some as yet unidentified bias causes differences. Comparing methods along Line P (over three years), we hypothesize that excretion of dissolved organic nitrogen, upwelling, bottle effects, mixing, and time of integration are the most important factors that cause disagreement between methods. End of bloom dynamics created an extreme case where method disagreement was most severe. Applying method comparison in the NE subarctic Pacific (August 2014 – June 2017) helps to understand what drives variability in primary production. Historical data show that chlorophyll-a is low and invariant offshore in the high nutrient low chlorophyll area (HNLC), where iron is limiting. We used satellites and models, which compare well with shipboard data, to expand our spatial and temporal coverage of the offshore HNLC area. Increased chlorophyll a is associated with higher production, higher salinity, and lower temperature. We hypothesize that iron can be supplied to surface waters by offshore fronts, using June 2015 and June 2016 as specific examples. Fronts are locations where temperature, salinity and/or density are rapidly changing, in this particular dissertation a 1°C change over 1/3 degree distance. We identified locations where fronts were located based on Mercator model sea surface temperatures and compared these features to satellite chlorophyll patterns. Our hypothesis is also supported by data from June 2017 where there were no fronts and chlorophyll was uniformly low. Future research should consider fronts as a possible mechanism for increasing productivity in the area. Identifying mechanisms that cause methods to disagree and then applying to biogeochemical regions allows for better understanding of carbon cycling. / Graduate / 2020-09-12

Phytoplankton dynamics and chemical characteristics of the euphotic zone were measured from 1998-2000 (an El Niño/La Niña cycle) at the 5 major stations along Line P. Near-shelf and offshore stations exhibited low seasonality in chlorophyll and moderate seasonality in particulate organic carbon (POC) production. During the 1998 El Niño, June was characterized by low chlorophyll and POC productivity due to nitrate depletion. In contrast, during the 1999 La Niña, and in 2000, higher POC productivity and nitrate occurred in June. During 1999, chlorophyll and POC productivity were similar to 1998 in late summer. Near-shelf biomass was highest in June and lowest in Feb. for the near-shelf stations. High nitrate, low chlorophyll (HNLC) stations had the highest chlorophyll in Feb. followed by June. The coccolithophore assemblage was usually numerically dominated by Emiliania huxleyi, particularly in June. Along the transect, coccolithophore abundance was much higher in June during the 1998 El Niño than in the 1999 La Niña, with Aug./Sept. abundance of both years being very low. Higher abundances were measured along the transect in June and the late summer of 2000 with sporadic ‘blooms’ of >1000 cells ml⁻¹ at some stations. Particulate inorganic carbon (PIC) production was high along the transect during June 1998, and low during both winters, June 1999 and during late summers of 1998 and 1999. There was an increase in diatom biomass and >20 µm POC production during the 1998 El Niño, specifically in the farthest offshore HNLC stations, yet diatoms were rarely found to dominate total phytoplankton biomass or production. However, there were some sporadic examples of anomalously high diatom biomass (carbon and abundance) as well as >20 µm POC production, specifically at P12 in Aug./Sept 2000. The same major diatom species were found throughout Line P (near-shelf, P16, and HNLC). Integrated silica production measured by ³²Si ranged from 0.2 to 4.7 mmol Si m⁻² d⁻¹ between 1999-2000. Silicic acid and nitrate were never limiting at all stations in Feb. and generally increased in concentration along Line P during all seasons.

Phytoplankton dynamics and chemical characteristics of the euphotic zone were measured from 1998-2000 (an El Niño/La Niña cycle) at the 5 major stations along Line P. Near-shelf and offshore stations exhibited low seasonality in chlorophyll and moderate seasonality in particulate organic carbon (POC) production. During the 1998 El Niño, June was characterized by low chlorophyll and POC productivity due to nitrate depletion. In contrast, during the 1999 La Niña, and in 2000, higher POC productivity and nitrate occurred in June. During 1999, chlorophyll and POC productivity were similar to 1998 in late summer. Near-shelf biomass was highest in June and lowest in Feb. for the near-shelf stations. High nitrate, low chlorophyll (HNLC) stations had the highest chlorophyll in Feb. followed by June. The coccolithophore assemblage was usually numerically dominated by Emiliania huxleyi, particularly in June. Along the transect, coccolithophore abundance was much higher in June during the 1998 El Niño than in the 1999 La Niña, with Aug./Sept. abundance of both years being very low. Higher abundances were measured along the transect in June and the late summer of 2000 with sporadic ‘blooms’ of >1000 cells ml⁻¹ at some stations. Particulate inorganic carbon (PIC) production was high along the transect during June 1998, and low during both winters, June 1999 and during late summers of 1998 and 1999. There was an increase in diatom biomass and >20 µm POC production during the 1998 El Niño, specifically in the farthest offshore HNLC stations, yet diatoms were rarely found to dominate total phytoplankton biomass or production. However, there were some sporadic examples of anomalously high diatom biomass (carbon and abundance) as well as >20 µm POC production, specifically at P12 in Aug./Sept 2000. The same major diatom species were found throughout Line P (near-shelf, P16, and HNLC). Integrated silica production measured by ³²Si ranged from 0.2 to 4.7 mmol Si m⁻² d⁻¹ between 1999-2000. Silicic acid and nitrate were never limiting at all stations in Feb. and generally increased in concentration along Line P during all seasons.

Phytoplankton dynamics and chemical characteristics of the euphotic zone were measured from 1998-2000 (an El Niño/La Niña cycle) at the 5 major stations along Line P. Near-shelf and offshore stations exhibited low seasonality in chlorophyll and moderate seasonality in particulate organic carbon (POC) production. During the 1998 El Niño, June was characterized by low chlorophyll and POC productivity due to nitrate depletion. In contrast, during the 1999 La Niña, and in 2000, higher POC productivity and nitrate occurred in June. During 1999, chlorophyll and POC productivity were similar to 1998 in late summer. Near-shelf biomass was highest in June and lowest in Feb. for the near-shelf stations. High nitrate, low chlorophyll (HNLC) stations had the highest chlorophyll in Feb. followed by June. The coccolithophore assemblage was usually numerically dominated by Emiliania huxleyi, particularly in June. Along the transect, coccolithophore abundance was much higher in June during the 1998 El Niño than in the 1999 La Niña, with Aug./Sept. abundance of both years being very low. Higher abundances were measured along the transect in June and the late summer of 2000 with sporadic ‘blooms’ of >1000 cells ml⁻¹ at some stations. Particulate inorganic carbon (PIC) production was high along the transect during June 1998, and low during both winters, June 1999 and during late summers of 1998 and 1999. There was an increase in diatom biomass and >20 µm POC production during the 1998 El Niño, specifically in the farthest offshore HNLC stations, yet diatoms were rarely found to dominate total phytoplankton biomass or production. However, there were some sporadic examples of anomalously high diatom biomass (carbon and abundance) as well as >20 µm POC production, specifically at P12 in Aug./Sept 2000. The same major diatom species were found throughout Line P (near-shelf, P16, and HNLC). Integrated silica production measured by ³²Si ranged from 0.2 to 4.7 mmol Si m⁻² d⁻¹ between 1999-2000. Silicic acid and nitrate were never limiting at all stations in Feb. and generally increased in concentration along Line P during all seasons. / Science, Faculty of / Botany, Department of / Graduate