Date of Award

Spring 2024

Project Type

Thesis

Program or Major

Earth Sciences

Degree Name

Master of Science

First Advisor

Kai Ziervogel

Second Advisor

Elizabeth Harvey

Third Advisor

Joseph Salisbury

Abstract

Phytoplankton play a crucial role in the biogeochemical cycles within the ocean and areresponsible for 34% of pelagic respiration. It is necessary to quantify plankton respiration to determine carbon budgets in marine systems and the production of accurate predictions of biogeochemical responses to climate change. The Gulf of Maine (GoM) is warming faster than 99% of the Global Ocean and by studying its response to climate change, it may be possible to predict future global changes. Field experiments were conducted in August of 2022 on NOAA’s third East Coast Ocean Acidification (ECOA-3) cruise which sailed in the Gulf of Maine and Scotian Shelf. Lab experiments were conducted with two local phytoplankton species, C. tenuissimus, and E. huxleyi cultured in 3 temperature conditions: 19°C, 22°C, and 30°C. Net community respiration (NCR) was calculated by measuring in-vivo electron transport system (ETS) activity using tetrazolium salt 2-para [ido-phenyl]-3[nitro-phenyl] (INT) substrate. NCR in the surface and subsurface waters were mainly driven by cells in the size fraction > 0.8 μm (i.e., > 50% of the NCR). This size fraction showed a positive correlation with chlorophyll a indicating that phytoplankton were a major fraction of this size class. Results from the culture experiments revealed that C. tenuissimus’ growth rates were significantly lower at 30°C compared to 19°C, and there was no significant difference between the growth rates for E. huxleyi at the 3 temperature treatments. No significant difference was found between temperature treatments for the volumetric or the cell-specific cellular respiration rates for C. tenuissimus while for E. huxleyi the 30°C temperature treatment had significantly higher volumetric and the cell-specific cellular respiration rates for. The NCR at the surface and subsurface in the Gulf of Maine in the summer of 2022 fall within the range of those observed in the culture experiments for C. tenuissimus and E. huxleyi. It is likely that if climate change continues its current trajectory, once the Gulf of Maine waters reach 30°C, the C. tenuissimus and E. huxleyi present in the surface and subsurface waters will experience much higher respiration rates.

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