Submarine volcanoes make up 80% of volcanic activity on Earth, but are relatively understudied due to the lack of real-time observations of eruptions and their inaccessibility, often several kilometers below sea level. Underwater volcanoes behave differently than their land counterparts due to the cold sea water surrounding them. Some submarine volcanism is violent as water pours into active vents, rapidly cooling lava and shattering it into fragments. Other eruptions can produce lava flows that extend tens of several kilometers before solidifying. The majority of submarine volcanoes occur in areas of tectonic activity such as mid-ocean ridges and hotspot island chains. One interesting site of submarine volcanic activity is the Submarine North Arch Volcanic Field 100 kilometers north of Oahu, Hawaii, hosting a few of the longest flows on Earth and covering over 25,000 kilometers². The field is associated with the Hawaii hotspots but the source of such extensive volcanism is poorly understood. Past studies have mapped the volcanic field flow but only at low resolution. The southeast portion of the field comprises of a series of lengthy flows, hypothesized to emanate from a 75 kilometer long fissure in the seafloor. However, the resolution of the maps was too low to test this theory. On the R.V. Thomas G. Thompson, our team used the high-resolution Kongsberg EM302 30-kHz multibeam echosounder to map the eastern boundary of the southeastern lava flow where the fissure would likely be located. Although area covered was limited by bad weather, we were able to map a 6 kilometer wide swath track extending 63 kilometers along the inferred fissure. We identified the presence of two features that were potentially part of the fissures. Each extends about 1-2 kilometers and comprise a 5 meter deep and 200-400 meters wide trough with a levee on either sides. 

Ocean-bottom seismometers (OBSs) are known to record puzzling signals termed short-duration events (SDEs) at frequencies of 4-18 Hz. SDEs are harmonic and usually have a duration of < 1 s, lack the P and S waves of local earthquakes, and individual events are never recorded on multiple OBSs. These signals have been attributed to either biological activity from animals bumping the seismic sensors or gas bubbles moving beneath the sea floor. In this study, we assess these explanations for SDEs using data from the Cascadia Initiative, a major OBS experiment along the continental margin of the Pacific Northwest that lasted from 2011-2015. After manually calibrating the acceptable trigger amplitude for each station, I ran a recursive short term/long term detector over the year they were deployed. Some shallow stations show a clear diurnal signal with more SDEs during the day, which is consistent with a biological origin, while others show no such pattern. SDEs are also observed on some of seismic stations on the Ocean Observatories Initiative Regional Cabled Array where the sensors are buried and protected from the biological bumps. I categorized the SDEs on representative stations based on parameters including the average frequency, bandwidth, number of peaks, and duration. This data will be used to determine whether the characteristics of the events show a pattern consistent with the biological or gas bubble hypotheses.

Located 100 km north of Oahu and over four kilometers of water, the North Arch Volcanic Field covers an area of 25,000 km² and includes the longest known underwater lava flow. A transect was mapped within the southernmost part of the field using a 30 kHz EM302 multibeam echosounder and 3.5 kHz Knudsen echosounders aboard the R/V Thomas G. Thompson. These surveys yielded a high-resolution bathymetric map and sub-bottom profiles that image shallow structures beneath the ship’s track. This research is investigating the extent and characteristics of these lava flows, as well as ability of Knudsen data to determine the location of flows. The seafloor is 300 meters shallower within the northern parts of the study area, as the transect moved onto the Hawaiian Arch. The lava flows here are more extensive and presumably closer to the eruptive source. Through the analysis of the Knudsen data, 29 lava flow crossings were found that vary in width and height. The lava flows have complex flow morphology, including different boundary structure, sediment pockets, complex flow paths, and elevation changes. There are two main areas of flows within the southern part of the study site with differing characteristics that may be related to the lava viscosity. The lava field is more variable than expected, which suggests that even in the small region sampled, it was formed by several effusive events over a period that had lava with different chemical properties. This work has shown that Knudsen data is extremely useful in classifying marine lava flows, and the further classification of the flow morphology of these lava flows can contribute to the understanding of the history of volcanism within the area, as well as marine effusive lava flows.

Prochlorococcus is a cyanobacterium smaller than 1 μm that accounts for much of the primary production in nutrient-poor areas such as the North Pacific Subtropical Gyre (NPSG). In the transition from the NPSG to more productive coastal regions, there are fronts that have sharp changes in chemical, physical, and biological properties. In more coastal, nutrient-rich conditions, larger phytoplankton are more abundant, including Synechococcus and picoeukaryotes. Data previously collected on cruises going north from the NPSG (the Gradients cruises) were compared to data I collected on the TN398 cruise going east from the NPSG to the California coast. A SeaFlow flow cytometer measured small phytoplankton, including Prochlorococcus, Synechococcus, and picoeukaryotes. Prochlorococcus was most abundant in nutrient-poor conditions in the NPSG, reaching a concentration of 300 cells/μL, and larger phytoplankton, including Synechococcus and picoeukaryotes, were most abundant in the coastal ocean and subpolar region. The diameters of Prochlorococcus, Synechococcus, and picoeukaryotes varied on a diel cycle that was most strongly observed in the gyre. The average diameter of Prochlorococcus and Synechococcus increased by about 0.2 μm outside the NPSG, while the diameter of picoeukaryotes observed by SeaFlow decreased by about 0.4 μm. Prochlorococcus abundance was negatively correlated with nitrate and nitrite. In the future, these variables could be compared seasonally, annually, and across ocean basins to better understand how these populations are responding to climate change.

The North Arch Volcanic Field lies north of O’ahu, covering 24,000 km² of seafloor. It is a part of the greater Hawai’ian Arch, a region of uplifted seafloor surrounding the Hawai'ian hotspot. The North Arch is a fairly recent discovery, with little known about it. It is a product of recent basaltic volcanism, the mechanism of which is not understood. The magnetic minerals found in basalts retain the signature of the Earth’s magnetic field at the time they cooled. Thus, basaltic lava flows generally have high remnant magnetization, distinguishing them from the surrounding, weakly-magnetized sediments. My objective was to use a magnetometer to assess the feasibility of using magnetic anomalies to determine the thickness of lava flows in the southern North Arch. On board the R/V Thomas G. Thompson, a sub-bottom profiler and multibeam sonar system were used to resolve lava flow boundaries while I collected data with a towed magnetometer. The ship followed 5 east-west track lines before heading north-west along an inferred rift on the seafloor, then west to exit the field. I obtained magnetic anomalies by correcting the raw magnetic data with the International Geomagnetic Reference Field and a time series from Honolulu’s magnetic observatory. I then used a modeling program to compare observed anomalies with those predicted for lava flows of varying thicknesses. A modeled flow along the northmost track line yielded a flow maximum thickness of 50 m, thinning to 5 km towards the east edge of the field. The results show that the magnetic anomaly produced by these flows was strong enough to be detected and yielded flow thicknesses of tens of meters that are consistent with other observations. This research demonstrates that magnetometry is an effective tool for studying the North Arch Volcanic Field and could be used on other submarine volcanic fields as well.

Ocean conveyor belt circulation is conceptually foundational in oceanographic education. It is the idea that oceans slowly overturn through the movement of deep water toward the equator and surface water toward the poles. Introductory courses often spend the majority of a semester building the skills required to understand the basics of this theory. Ocean circulation is also typically covered through multiple courses to build upon its complexity through different study lenses. The multi-dimensional concept of ocean circulation is commonly conveyed through 2D diagrams and animations rather than presenting ideas in a 3D space that allows students to form connections between theory and physical space. Students were asked to interact with a 3D printed model that recreates circulation diagrams by connecting cross-sections of oceanographic data to specific locations on the model. Furthermore, students were asked to describe how perturbations to surface conditions could change ocean stratification and how water circulates based on its temperature and salinity. Previous 3D printing experience allowed us to expand students’ experiences while struggling to parse these interdisciplinary oceanographic topics. Here we show that using a physical model in teaching thermohaline circulation enhances the speed and depth at which students understand ocean circulation compared to the traditional 2D approach. Surveys were given to assess students’ understanding of the driving factors behind thermohaline circulation prior to and after interacting with the model. Preliminary results show that students can better connect oceanographic concepts taught in lectures to data and locations essential to ocean circulation after completing exercises that ask them to interact with the model. We anticipate students to exhibit further proficiency in concepts related to ocean circulation after interacting with this model. We also expect to find that students will express a desire to see the utilization of similar models in more of their core oceanography courses.

Community composition and structure of modern benthic foraminiferal assemblages are commonly used as indicators of integrative water quality. The San Juan Archipelago is a tidally mixed estuarine environment located in the Salish Sea. This is an oceanographically complex area due to ocean input from the Strait of Juan de Fuca and estuarine input from the Fraser River. To assess the feasibility of using foraminifera as water quality indicators, foraminiferal assemblages from four oceanographically distinct locations in the San Juan Archipelago were collected and subsequently identified to pair water conditions with associated differences in assemblage. I carried out a survey of foraminiferal tests from Rosario Strait, Strait of Juan de Fuca, and San Juan Channel. Density of the number of tests decreased in high current environments and water-column stratification had no impact on assemblage. Abundance of Lobatula lobatula and Rotalinoides gaimardii were significantly correlated with oxygen, temperature, salinity, and nitrate. Depth and individual water conditions were observed to impact diversity of foraminiferal assemblage more than stratification. Foraminifera are incredibly resilient and present in most sediments of the San Juan Archipelago allowing foraminiferal assemblage to be used as a tool for water quality assessment in the San Juan Archipelago based on the abundance of species like L. lobatula and R. gaimardii.

Plastic pollution is a growing concern in the microecology of the oceans. Studying bacteria colonization rates on plastic provides one way of understanding of how toxic debris can move through the food chain through ingestion. This process of toxins moving through the food chain is called biomagnification and can eventually reach humans. To evaluate bacterial colonization rates, I collected seawater in the coastal waters of Hawaii and near the Pacific garbage patch (GPGP). Seawater was intermixed with 5 different kinds of clean plastics then timed to determine how long it took bacteria to colonize the plastic surfaces. Bacteria on the plastic were counted under an epifluorescence microscope then divided by the time of colonization to determine the rate. Alongside the colonization rate, surface microplastics were collected with a manta net; then sized and classified with a dissection microscope. Seawater was collected from a Niskin bottle attached to a CTD (Conductivity, Temperature, and Density sensors) rosette to calculate bacterial abundance with the use of a Guava flow cytometer. The findings of the research displayed little to no correlation between surface bacterial abundance and plastic density, with an R2 value of 0.1072. Bacteria were found to colonize plastics at 48 and 96 hours in the waters near the Pacific garbage patch with a rate of 7.4E+04 cells/mm. The colonization rates and plastic abundance support evidence of plastics being integrated into the ocean ecology.
 

Global cycling of elements like carbon, nitrogen, and iron have key roles in maintaining the biosphere. These and other micro- and macro-nutrients undergo important reduction-oxidation and acid-base transformations in the environment. Biologically, iron (Fe) and manganese (Mn) are utilized by microbes as cofactors in many essential proteins and enzymes including nitrogenase, ferredoxin, peroxidase, cytochromes, and phosphotransferase. These elements (most notably Fe) can often limit microbial growth in large regions of the ocean because of their trace environmental concentrations, or due to structural bioavailability, or competitive microbial uptake and utilization. This can impact key ecosystem and cellular processes, including chemosynthetic carbon fixation at hydrothermal vents, nitrogen species reduction, and metabolic electron transport. Here we use flow cytometry measurements (FCM) to quantify bacteria and archaea from hydrothermal vent plumes along the Southern East Pacific Rise. We compare patterns in microbial abundance with total dissolvable Fe concentrations (predominantly Fe3+, including dissolved and labile particulate Fe) at the same locations. I find that bacterial abundance is most strongly related to trace-concentration of Fe below 400nM, and that similar relationships exist with trace methane (CH₄) and dissolved Mn concentrations. These findings suggest that microbial abundances in vent plumes could be partially explained by trace element and methane distributions, but further research is required to disentangle whether these important substrates are covarying with other biochemical factors impacting microbial growth and metabolism in these dynamic environments.

Photosynthesis and organic matter production by photoautotrophs in the upper ocean are fueled by sunlight. In previous research, environmental metabolite concentrations in the sunlit ocean have been found to display significant 24-hour periodicity. Prochlorococcus is a marine cyanobacteria that is the smallest and most abundant photosynthetic organism on Earth and is a key primary producer in the ocean’s vast oligotrophic gyres. Past studies employing transcriptomics and flow cytometry-based approaches revealed that cell division, metabolism, and gene expression of Prochlorococcus are synchronized with the daily light-dark cycle, but the impacts of these diel changes on the Prochlorococcus metabolome remain poorly understood. Here we investigate how levels of particulate metabolites in Prochlorococcus vary over simulated light-dark cycles in a non-axenic culture. We grew Prochlorococcus MED4 and its associated consortium of heterotrophic bacteria over daily light-dark cycles in culture and sampled for particulate and dissolved metabolites every 6 hours for a total of 48 hours. We extracted metabolites using a modified Bligh and Dyer extraction and quantified metabolites using liquid chromatography paired with mass spectrometry. To detect diel patterns in metabolite concentrations, we used Rhythmicity Analysis Incorporating Nonparametric methods to identify significant changes in Prochlorococcus’ metabolome over the light-dark cycle. Sucrose, a disaccharide sugar, varied over the diel cycle and peaked at the end of the light cycle, highlighting the use of this compound for energy storage in Prochlorococcus. Glutamine, a metabolite associated with nitrogen assimilation, displayed diel variation and peaked at midnight, lagging the peak in sucrose by 6 hours. These results indicate diel partitioning of Prochlorococcus’ metabolic functions related to energy storage and nitrogen assimilation. This diel partitioning mirrors prior results observed in environmental metabolomes and transcriptomes.