Advancing climate-critical ocean carbon observations through new applications of autonomous technologies

Abstract

The ocean is a critical component of the global carbon cycle. As global anthropogenic carbon emissions continue to rise understanding the ocean’s role in carbon cycling has become a major focus for scientific observation and intervention. The marine carbonate system underpins the central role of the ocean both in moderating atmospheric CO2 and ocean pH, yet it remains poorly constrained in space and time, particularly in dynamic coastal environments. Traditional ship-based approaches constitute the "gold-standard" data quality but are sparse, seasonally biased, and resource-intensive, highlighting the urgent need for increased high-resolution observational strategies. In this thesis I present new methodological approaches through the use of cutting-edge autonomous technologies to address these gaps and advance the understanding of ocean carbon. Here, I demonstrate that autonomous carbonate observations can approach the quality of traditional methods while delivering unprecedented spatiotemporal coverage at reduced cost and carbon footprint. Lab-on-Chip pH and TA sensors on the Autosub Long Range AUV yielded the first high-resolution carbonate characterisation from autonomous sensors, detecting fine-scale coastal biogeochemical processes with ship-comparable quality. An extended AUV deployment with dual pH sensors resolved carbonate dynamics and air–sea CO2 fluxes while critically assessing sensor corrections and uncertainties. Finally, multi-month autonomous reef observations in the Red Sea---including the first stand-alone TA sensor on a coral reef---captured diel and seasonal variability in different reef environments and provided carbonate chemistry characterisation to an undersampled region. Collectively, this work advances both understanding of ocean carbon dynamics and the capabilities of autonomous observation. I highlight both the scientific insights (ranging from regional carbon cycling to reef metabolic processes) and the methodological advances required for climate-critical ocean carbon observation. By confronting the observational gaps of the marine carbonate system, my doctoral thesis establishes novel autonomous technologies as a defensible strategy to understand, monitor, and respond to ocean chemistry in a changing climate.

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Identifiers

ORCID for Emily Madison Hammermeister: orcid.org/0000-0002-1739-761X

ORCID for Adrian Nightingale: orcid.org/0000-0003-2445-4827

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