Date of Award

2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Oceanography

Specialization

Biological Oceanography

Department

Oceanography

First Advisor

Chris Roman

Abstract

Biological processes in midwater habitats -- ocean areas between the sunlit surface layers and sea floor -- are critical drivers of ocean biogeochemical cycling, oxygen availability, fish population dynamics, and ecological interactions over a wide range of scales. Achieving high-resolution observations of the environmental and biological heterogeneity in the ocean's interior is important for understanding the status and evolution of the earth system at large. Traditional ocean sampling platforms (e.g. net systems, moored and shipboard sensors), are often unable to resolve marine biota at fine (cm-m) scales and over submesoscale (sub-km to kms) survey areas comparable to the relevant variability in their physical environment. Shipboard mounted acoustic echosounders are commonly used to resolve biological data in the open ocean but record coarse measurements below 300m depth, due to acoustic attenuation, and do not collect matching environmental data. Existing towed sensor platforms are limited in their spatial and temporal resolutions due to constraints from tow cable dynamics, and autonomous platforms such as AUVs and gliders are often limited by their speed and endurance.

The development of sensor-based field surveys that can achieve concurrent biological and environmental measurements over large sampling spaces at fine scales allows for improved characterization of these ecosystems. Studies employing these modern survey tools have shown that biological assemblages in marine ecosystems are often characterized by extreme spatial and temporal heterogeneity, and respond to fine environmental gradients, submesoscale physical processes (e.g. eddies, fronts, and internal waves), diel rhythms, and ephemeral opportunities for resource exploitation. This thesis work seeks to both derive techniques supporting the use of new imaging and acoustic sensor platforms to achieve detailed biological-environmental coupled datasets and to use the data to assess the linkages between animal habits and local hydrography in diverse midwater habitats. Collectively the results from this project will help to further the technology-enabled exploration of the vast but di cult to observe midwater habitat and will contribute several novel characterizations of biological-environmental coupled dynamics in diverse epi and mesopelagic ecosystems.

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