Ocean optics: Development of glider-based productivity analysis in BC waters using backscatter
Date
2025
Authors
Koopmans, Emily
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Abstract
The ocean plays a crucial role in regulating atmospheric carbon dioxide yet quantifying the processes that govern its carbon storage remains a challenge. The biological pump, which converts dissolved carbon into organic particles through biological processes, is a key component of this cycle. While some particles remain suspended in the upper ocean, others sink, either individually or as larger aggregates, contributing to long-term carbon sequestration. Understanding the distribution and size of these particles is essential, but measurements are difficult to obtain since particle dynamics fluctuate with biological activity, ocean currents, and seasonal changes. Optical backscatter offers a valuable tool to address this challenge.
We developed a method to process backscatter sensor data from autonomous ocean gliders, adapting a technique originally designed for Argo floats. Our approach partitions raw backscatter into three components: scattering from large aggregates, smaller particles, and instrument noise. A two-filter method was used to isolate scattering from small particles, while the deepest backscatter measurements provided an estimate of background noise. The remaining signal was attributed to large aggregates.
We applied this method to data from a Canadian-Pacific Robotic Ocean Observing Facility (C-PROOF) glider mission in offshore British Columbia waters. By comparing size-resolved backscatter and chlorophyll fluorescence, we observed distinct differences in particle dynamics, with small-particle backscatter strongly correlated with chlorophyll and large-particle backscatter showing weaker associations. We identified contrasting high-productivity regions: one dominated by smaller particles, and another dominated by large aggregates. These patterns suggest that areas with similar chlorophyll concentrations can differ significantly in their potential for carbon export, depending on particle composition and sinking behavior.
This approach also revealed important oceanographic features, including a subsurface chlorophyll maximum, sediment resuspension layers, and a small but persistent zone of elevated productivity likely influenced by large-scale ocean circulation. These features highlight how regional carbon export can be enhanced by subtle physical changes such as fronts or circulation boundaries—emphasizing the need to consider both biological and physical drivers when studying oceanic carbon cycling.
By enabling size-resolved analysis of particulate matter, our method enhances the utility of gliders for carbon cycle research. Its application across other missions could help identify export hotspots, track seasonal variability, and improve estimates of oceanic carbon sequestration in a changing climate.
Supervisor: Roberta Hamme
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Keywords
optical backscatter, carbon pump, ocean glider, carbon export, particulate organic carbon, chlorophyll