Beckett C. Colson

Many in situ dissolved gas instruments use a membrane inlet to extract gas from water enabling measurement in the gas phase. However, mass transport across membranes is slow, making it difficult to build instruments with fast time responses. Several approaches exist to improve time response, including pulling vacuum to enhance gas flux, but the trade-offs between different approaches are unclear. Starting from first principles, we present a set of analytical models describing the operation of four different approaches for operating a membrane-based dissolved gas instrument. Using these models, we obtain the steady state and dynamic performance characteristics of each approach, and identify design trade-offs between speed, sensitivity, and complexity. Insights from these models enable physics-based design decisions and design optimization instead of instrument designers needing to rely on empirical methods.

The Cold Seeps Extreme24 Expedition was the second leg of two expeditions, which form part of the University of Tromsø’s Extreme 24 project. The expedition focused on cold seeps sites characterised by methane emissions in several localities in the Barents Sea. The expedition is a research initiative (PI G. Panieri) hosted by the Department of Geosciences, part of the Faculty of Science and Technology at UiT, the Arctic University of Norway, situated in Tromsø, and involved partners from different research institutes and universities around the world and used the REV Ocean Remotely Operated Vehicle (ROV) Aurora. The expedition has been developed by leveraging the extensive knowledge gained from two significant projects funded by the Norwegian Research Council: CAGE (Centre for Arctic Gas Hydrate, Environment and Climate) and AKMA (Advancing Knowledge of Methane in the Arctic), both hosted at the Department of Geosciences at UiT. These projects have provided fundamental understandings to define the objectives and methodologies used during the EXTREME24 expedition, aiming to broaden our understanding of Arctic extreme environments.

The AKMA3 oceanographic expedition (29th April–10th May) is part of the Advancing Knowledge of Methane in the Arctic, a project funded by the Norwegian Research Council (287869). The main aim of AKMA is to develop a long-term, multidisciplinary education, and research collaboration focused on Arctic methane sources, processes, ecosystems, and geological history to provide exceptional training for the next generation of experts in Arctic marine sciences and greenhouse gas phenomena. The AKMA3 oceanographic expedition focuses on three objectives: SCIENCE: Focus on the interplay between changing ocean conditions and the physical, biological, and chemical response of extreme environments (methane and oil seepage sites) through a multidisciplinary study of sites in the Barents Sea. Research activities: study sediment-sea-air greenhouse gas exchange; conducting water-column profiling of CH4; gas source analyses; biological and sediment sampling. EDUCATION: This high-level science on this cruise also includes sea-going training for students to develop their knowledge in collecting, curating, and processing samples and data, providing opportunities to fully engage in marine science. OUTREACH: To generate enthusiasm and interest in research expeditions with students and to promote a deeper understanding of science and its applications.

To predict and mitigate anthropogenic impacts on the ocean, we must understand the underlying systems that govern the ocean’s response to inputs (e.g. carbon dioxide, pollutants). Analytical models can be used to generate predictions and simulate intervention strategies, but they must be grounded with empirical observations. Unfortunately, there exists a technological gap: in situ instrumentation is often lacking or nonexistent for key parameters influenced by anthropogenic inputs. While discrete bottle samples can be collected and analyzed for these parameters, their limited spatiotemporal resolution constrains scientific inquiry. To help fill the technological gap, this dissertation presents the development of instrumentation for the ocean inorganic carbon system and microplastics. The first few chapters present the development process of CSPEC, a deep-sea laser spectrometer designed to measure the ocean carbon system through alternating measurements of the partial pressure of carbon dioxide (pCO2) and dissolved inorganic carbon (DIC). CSPEC uses tunable diode laser absorption spectroscopy (TDLAS) to measure the CO2 content of dissolved gas extracted via a membrane inlet. Chapter 2 derives membrane equilibration dynamics from first principles, thus enabling informed design decisions. The analytical results showed that cross-sensitivity to other dissolved gases can be introduced by the equilibration method, regardless of the specificity of the gas-side instrumentation. A new method, hybrid equilibration, leverages the membrane equilibration dynamics to improve time response without incurring cross-sensitivity. Chapter 3 presents POCO, a surface pCO2 instrument that employs TDLAS and a depth-compatible membrane inlet. Through laboratory and field-testing, POCO demonstrated that hybrid equilibration overcame the gas flux limitation of deep-sea membrane inlets. Chapter 4 presents CSPEC, which successfully mapped the carbon system near different hydrothermal features at 2000 m in Guaymas Basin, becoming one of the first DIC instruments field-tested at depth. Chapter 5 introduces impedance spectroscopy for quantifying microplastics directly in water. Microplastics were successfully counted, sized, and differentiated from biology in the laboratory: a step toward in situ quantification. The analytical tools and measurement systems presented in this dissertation represent a significant step towards increasing the spatiotemporal resolution of carbon system and microplastic measurements, thus enabling broader scientific inquiry in the future.

Microplastics (MPs) have been found in aqueous environments ranging from rural ponds and lakes to the deep ocean. Despite the ubiquity of MPs, our ability to characterize MPs in the environment is limited by the lack of technologies for rapidly and accurately identifying and quantifying MPs. Although standards exist for MP sample collection and preparation, methods of MP analysis vary considerably and produce data with a broad range of data content and quality. The need for extensive analysis-specific sample preparation in current technology approaches has hindered the emergence of a single technique which can operate on aqueous samples in the field, rather than on dried laboratory preparations. In this perspective, we consider MP measurement technologies with a focus on both their eventual field-deployability and their respective data products (e.g., MP particle count, size, and/or polymer type). We present preliminary demonstrations of several prospective MP measurement techniques, with an eye towards developing a solution or solutions that can transition from the laboratory to the field. Specifically, experimental results are presented from multiple prototype systems that measure various physical properties of MPs: pyrolysis-differential mobility spectroscopy, short-wave infrared imaging, aqueous Nile Red labeling and counting, acoustophoresis, ultrasound, impedance spectroscopy, and dielectrophoresis.