Saltwater estuaries can experience high turbidity levels due to river input and tidal influences. Turbidity is a measure of inorganic and organic particles suspended in the water column. Reduced light penetration due to higher turbidity levels can contribute to decreased levels of primary production and the introduction of harmful pathogens to the environment. Understanding the relationship between river discharge, tides and turbidity levels could lead to a better understanding of the causes of turbidity in estuaries such as Possession Sound, WA. I hypothesize that higher current velocity contributes to higher turbidity levels. I analyzed data from a moored Acoustic Doppler Current Profiler (ADCP) and a Conductivity, Temperature, Depth (CTD) sensor located in the Everett Marina. ADCP and turbidity data were collected every 15 minutes, 24 hours a day, from 2017 to 2021. Preliminary results suggest that higher current velocity correlates to higher turbidity levels. Future research looks to discover how river discharge, tides and seasonal variance play into turbidity spikes.

Nutrients and CO₂ are important oceanographic variables, as they provide information which can be used to understand phytoplankton abundance and processes such as the oceanic carbon cycle. Therefore, as climate change impacts ocean systems, it is increasingly important to measure how nutrient and CO₂ concentrations in the ocean change over time and space. This study measured pCO₂ (which takes into account temperature, total CO₂, salinity, and alkalinity of the water), nitrate, phosphate and silicate concentrations in the western equatorial Pacific (5S-5N along 167W) in January 2024. Over space, pCO₂ and nutrients were analyzed for correlation with physical processes, primarily upwelling, using sea surface temperature (SST) and mixed layer depth. To determine the relationship of pCO₂ and nutrient concentrations to the biomass of microorganisms, correlations with fluorescence and beam transmission were also analyzed over space. Over time, pCO₂ was compared to atmospheric CO₂ and El Nino Southern Oscillation (ENSO) state to determine correlations between temporal pCO₂ trends and atmospheric phenomena. pCO₂ surface concentrations in the western equatorial pacific were found to have increased from 1983 to 2024 at an average rate of 2.02 +/- 0.034 ppm/yr and had a positive correlation with increasing average atmospheric CO₂ (R = 0.71, p-value < 0001). Spatially, surface pCO₂ and the macronutrients nitrate, phosphate, and silicate in the upper 200 m showed similar patterns from 5S to 5N along 167W. The concentrations of nitrate and phosphate had a significant negative correlation to mixed layer depth (R = -0.4, p-value < 0.001) and nutrients and pCO₂ had a significant negative correlation to sea surface temperature (p-value < 0.001). They peaked from 0-2N due to upwelling and exhibited smaller secondary peaks around 3S and 3N, likely due to mixing caused by north and south subsurface countercurrents. These results reinforce the importance of physical oceanic and atmospheric processes as a control for nutrient and inorganic carbon cycles in the western equatorial Pacific.

The paradigm for manganese (Mn) cycling in the marine environment has shifted over the past two decades to include not only the +IV and +II oxidation states. It is now recognized that dissolved Mn(III) can also exist when stabilized by organic ligands. Mn is critical for sustaining life and influences the cycling of many other bioactive elements. Because of this, further research is needed for understanding how Mn cycles in the environment, both between physical and chemical phases. My project aimed to look at how Mn cycles between dissolved and particulate phases and its three environmentally relevant oxidation states along the salinity gradient of the Mississippi River delta and what role organic ligands play in mediating Mn transformations. I hypothesized that the salinity gradient would influence the availability of organic ligands, which would promote the oxidation of dissolved Mn(II) and particulate Mn oxides (MnOx), making the cycling of Mn during estuarine mixing more complex than previously understood. To test this, I collected water from the Mississippi River and the Gulf of Mexico to conduct a mixing experiment to model the salinity gradient. UV-Vis spectrophotometry was used to analyze particulate and dissolved Mn speciation as well as the characteristics of the organic matter present. Inductively coupled plasma-mass spectrometry was used in analyzing dissolved Mn and Mn flocculants. Preliminary results show increases of dissolved Mn during mixing, and potential loss of particulate MnOx. Combined, these suggest redox cycling of Mn during estuarine mixing impacts its solubility and ultimately transport to the Gulf of Mexico. This region experiences heavy nutrient loading that leads to seasonal hypoxia. Understanding the cycling and solubility of Mn is imperative because it has broader implications for redox processes and element cycling in the Northern Gulf of Mexico, especially during hypoxic events.

Over the last two decades, the threat of climate change has inspired significant research in the Salish Sea. Understanding trends and correlations between water temperature, dissolved oxygen (DO), and chlorophyll levels can help us understand how climate change and other anthropogenic activity has already affected the Salish Sea. My reseach focuses on seasonal and annual trends of water temperature, DO, and chlorophyll levels between 2019 and 2023 in Possession Sound, located in Everett, Washington. This longterm data-stream is generated by the Ocean Research College Academy, collected autonomously every 15 minutes by a pair of EXO sondes that are moored at Mount Baker Terminal and Everett Marina. My goal is to understand the relationship between water temperature, DO, and chlorophyll seasonally and historical trends over multiple years in Possession Sound. Preliminary figures and outside research have shown fairly consistent seasonal cycles for temperature and chlorophyll. DO trends are not as clear and data suggest significant variation is occurring within a short time frame. Future reseach may include comparing river discharge data to water chemistry data, however a more comprehensive understanding of specific inputs to the Snohomish River system is needed to draw solid conclusions about the affects of climate change.

Marine heterotrophic bacteria play a pivotal role in microbial community dynamics. This study aims to understand interactions within the microbial community of the oligotrophic (nutrient-poor) equatorial Pacific, specifically investigating how heterotrophic bacteria respond to the growth of autotrophic picophytoplankton. This experiment attempts to provide a more faithful representation of in-situ conditions, overcoming previous difficulties in capturing the dynamic behavior of microbial communities in the field. A novel methodology utilizing continuous chemostats with natural communities in the field accomplishes this objective. Three growth chambers were employed, two as chemostat systems and one in batch culture mode. All three growth chambers contained the natural microbial community that passed through a 3 µm pore-size filter. Chemostat systems continuously received 0.2 µm-filtered seawater (without microbes) while an equivalent volume was removed from the growth chamber simultaneously. Dissolved inorganic nutrients required by autotrophs – silicate, phosphate, and nitrate – were added to one of the chemostat’s 0.2 µm filtered media reservoir. This methodology was compared to a traditional batch culture, where nutrients were added to the growth chamber once, at time-zero. Cultures followed a 16-hour on/8-hour off light/dark cycle using LEDs, simulating the equatorial Pacific day/night cycle. Community responses were measured by continuous optical density measurements (OD), with endpoint subsamples analyzed for microbial abundance and DNA content using flow cytometry. Distinct day/night responses were observed in all cases, with the nutrient-enriched chemostat showing the most pronounced response. Overall, the results provide new insight into the linkages between marine autotrophic and heterotrophic microbes, while demonstrating an effective new methodology for examining microbial community responses to added nutrients. Thus, this study not only advances our understanding of microbial community dynamics in the oligotrophic equatorial Pacific but also introduces a novel experimental method that can be applied across a diversity of marine and aquatic environments.

Marine cyanobacteria have developed many genetic defenses in response to viral infection. Similar defense genes have been found in diverse groups of cyanobacteria, suggesting different modes of evolution for defense genes. Berube et. al (2018) identified novel cyanobacterial clusters of orthologous genes (CyCOGs), families of genes with similar genetic sequences. However many of these CyCOGs remain uncharacterized. The goal of my study was to characterize an uncharacterized CyCOG called 60001830, which is expressed in the marine cyanobacteria Prochlorococcus and Synechococcus, and when expressed is correlated with the genes of viruses that infect cyanobacteria (cyanophages). This suggests CyCOG 60001830 has an adaptive response to the presence of cyanophages, which would make it a family of defense genes. Using phylogenetic analysis, I resolved the evolutionary history of CyCOG 60001830 by comparing it to the evolutionary history of a key gene in host genomes. I compared the phylogeny of CyCOG 60001830 to the phylogeny of RecA, a highly conserved and essential gene present in all Prochlorococcus and Synechococcus species because of its key role in DNA repair and/or maintenance. CyCOG 60001830 does not share the same evolutionary pattern as RecA, which suggests that it does not follow a pattern of vertical gene transfer but rather horizontal gene transfer, genes being exchanged between neighboring bacteria. Viral defense genes evolve rapidly in an evolutionary arms race between bacteria and phages, so CyCOG 60001830’s evolutionary pattern makes sense as horizontal gene transfer operates faster than vertical gene transfer.