Date of Award

Summer 8-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean & Earth Sciences

Program/Concentration

Oceanography

Committee Director

Alexander B. Bochdansky

Committee Member

Tal Ezer

Committee Member

Richard C. Zimmerman

Committee Member

Charles I. Sukenik

Abstract

Particle concentration and sinking velocity control the export flux and transfer efficiency of the biological carbon pump, and are therefore key parameters in ocean biogeochemical models. Gel-like particles form an important part of the particulate organic carbon pool, but their contribution is difficult to quantify because they are fragile and nearly transparent to conventional optical instruments. Here, a focused shadowgraph imaging system (FoSI) was applied to marine gel research to examine the ecological significance, distribution, and transport of gel-like particles along a transect from the Azores to the upwelling region off northwest Africa.

A new image processing protocol was developed for FoSI to detect small, low-contrast particles, combining illumination correction, image subtraction, edge detection, and artifact removal to resolve particle edges for segmentation. Gel-like particles showed distinct geometrical characteristics between depth layers and regions, and were one to two orders of magnitude more abundant than opaque particles. The same system was deployed at 600 m in the Sargasso Sea off Bermuda to relate sinking velocity to particle size and morphology for particles 24–631 μm. Size alone explained 25% of the variance in sinking velocity, while adding particle characteristics through deep learning increased the predictive power by nearly 29%. Because mixing transports small particles efficiently, a one-dimensional Mellor–Yamada turbulence model was applied to resolve the mixed layer pump. Strong particle detrainment in winter and spring injected slow-sinking particles from the surface into the mesopelagic zone, with weaker detrainment in summer, providing an additional organic carbon source to the deep sea.

Small and gel-like particles may therefore contribute more to the biological carbon pump than previously recognized, indicating that their role in marine biogeochemical cycling has likely been underestimated. Further quantification of this elusive particle pool is needed, as improved estimates of its abundance, distribution, and vertical transport may require reassessment of particulate organic carbon inventories and their parameterization in ocean biogeochemical models.

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DOI

10.25777/qwnc-ab63

ISBN

9798193214526

ORCID

0000-0002-6751-6250

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