Date of Award

Fall 2023

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Ocean and Earth Sciences

Committee Director

Margaret R. Mulholland

Committee Member

Sophie Clayton

Committee Member

Eileen E. Hofmann

Abstract

The southern Mid-Atlantic Bight (MAB) near Cape Hatteras, NC, USA, is likely a hotspot for the episodic export of carbon-rich shelf waters to the open ocean. Over a 2 year period, from March 2017 to May 2019, Spray gliders repeatedly occupied transects, along the slope and across the shelf, generating high-resolution chlorophyll fluorescence (fChl) data in the southern MAB. This study implements an fChl calibration method utilizing remotely sensing ocean color as a standard. We validate the method’s utility by demonstrating a reduction in post-calibration cross-mission fChl variability and demonstrating close correspondence between the calibrated fChl data and an in situ chlorophyll measurements. Using the calibrated fChl data, we calculate the mean and standard deviation of fChl for the study region on both annual and seasonal time scales. In general, we found that fChl concentrations were highest in the winter-spring season, followed by the summer, with the lowest mean fChl observed in fall. Spatially, high mean concentrations of fChl are associated with a relatively greater chlorophyll at depth in spring-winter, from the surface down to 250 m. High mean concentrations of fChl are confined to a subsurface layer from 10 m to 40 m in the summer, and fall’s highest mean concentrations of fChl are found in the top 50 m in fall. The highest variability in fChl was observed in the winter-spring season, with peaks near the surface and between 150m and 250m at the southern end of the slope transect, near the Gulf Stream wall. We interpret this high variability in fChl as an indication that episodic fluxes of high chlorophyll concentrations, termed as “deep chlorophyll events”, may be occurring in this location. To support this idea, we identified 10 individual deep chlorophyll events based on fChl (> 0.75 mg m-3) and depth (>100m) thresholds and found that the events occurred primarily in winter-spring; with a small number also identified in summer and none in fall; and have similarities with previously recognized mechanisms of shelf water cascade dynamics and MAB cold pool export.

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DOI

10.25777/z7sb-sf94

ISBN

9798381447859

ORCID

0000-0002-8068-0477

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