Date of Award

Fall 2023

Project Type

Thesis

Program or Major

Earth Sciences

Degree Name

Master of Science

First Advisor

Douglas Vandemark

Second Advisor

Atsushi Matsuoka

Third Advisor

Joseph Warren

Abstract

Variability in light field penetration into the ocean alters both radiant heat flux and oceanic primary production. Both are increasingly important in the context of quantifying biologically-mediated atmospheric carbon fluxes and sea surface temperature increase in a changing climate. Accurate determination of light penetration into the upper ocean depends upon accurate estimates of the depth-resolved water absorption and attenuation properties through the water column, properties that are often assumed homogeneous vertically and slowly variant in time. This thesis explores all-new Gulf of Maine datasets collected using a moored vertical profiler that provides sub-hourly light attenuation profiles with sub-m vertical resolution through the upper 50-100 m of the ocean. These data were gathered as part of the UNH Acoustic Environmental Observing Network project and cover several extended periods and three seasons in 2021-2022. The data allow examination of temporal variability in light field properties on timescales from daily to seasonal. Controlling factors addressed include solar zenith angle, cloud fractional coverage, ocean mixed layer dynamics, and biogenic parameters including Chlorophyll and particles. Measurements were made using a wave-powered WireWalker system that includes a PAR (?= 400 - 700 nm) planar solar irradiance sensor as well as a CTD and bio-optical packages. Focus is on two common light attenuation metrics, the e-folding (first optical) depth of blue-green light and the euphotic depth (1% of surface PAR). The former is closely related to the maximum depth seen using ocean color satellites. The continuous profiler time series allows estimates of hourly Chla and particle backscatter change above this e-folding depth that can be inferred from space, and also the frequently large fraction that lies below this depth. The thesis examines both parts of the water column, as well as the general variability in light penetration due to time variable change associated with the Gulf of Maine tides, storm mixing, and seasonal changes. Results highlight the need for depth-resolved measurements of chlorophyll and particle backscatter from in-situ Eulerian platforms as well as with emerging technologies including lidar remote sensing.

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