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Date of Award

Spring 2025

Document Type

Masters Thesis

Department or Program Affiliation

Environmental Science, Marine and Estuary Science Program

Degree Name

Master of Science (MS)

Department

Environmental Sciences

First Advisor

Strom, Suzanne L., 1959-

Second Advisor

Love, Brooke

Third Advisor

Olson, M. Brady (Michael Brady)

Abstract

The Northern Gulf of Alaska (NGA) is a productive subarctic ecosystem that supports a robust food web including many ecologically and commercially important fish, bird, and mammal species. Especially in summer, picophytoplankton (< 3 µm) can be an important component of the producer community at the base of this food web. Current paradigms imply that picophytoplankton do not contribute significantly to carbon export to deeper waters. However, recent findings in the Gulf of Alaska show that summer phytoplankton communities can be associated with high vertical exports. This study's objective was to compare estimates of picophytoplankton primary productivity and vertical export in the NGA, using the abundant picocyanobacteria Synechococcus spp. as the model organism. The primary production, grazing rates, abundance, pigment content, distribution, and vertical export rates of Synechococcus were studied during a summer 2023 oceanographic research cruise to the region. We conducted on-deck incubation experiments and sediment trap deployments, with fluorometry and flow cytometry used to assess Synechococcus growth rates and quantify the pigment phycoerythrin as a biomarker for Synechococcus export. Primary production showed cross-shelf gradients associated with iron availability. Stations furthest offshore had lower iron concentrations, cell abundance and primary productivity than stations nearshore and on the shelf break. Export ratios ranged from 4%-14% across stations, such that Synechococcus export was a small but significant portion Synechococcus production in summer 2023. Fecal pellets and aggregates were the main mechanism of vertical transport, with fecal pellets more important closer to shore. Phytoplankton communities are predicted to shift to dominance by smaller phytoplankton, including picophytoplankton, as ocean warming continues. Understanding the relationships between primary productivity and vertical export of picophytoplankton is critical to understanding the ecosystem of the NGA and for predicting how much material will be transported to the benthic ecosystem under future scenarios.

Type

Text

Keywords

Synechococcus, vertical export, primary productivity, Gulf of Alaska, export ratios, phycoerythrin, phytoplankton, picophytoplankton

Publisher

Western Washington University

OCLC Number

1523157201

Subject – LCSH

Phytoplankton--Alaska--Alaska, Gulf of; Primary productivity (Biology)--Alaska--Alaska, Gulf of; Food chains (Ecology)--Alaska--Alaska, Gulf of

Geographic Coverage

Alaska, Gulf of (Alaska)

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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