Date of Award

Spring 2021

Project Type

Thesis

Program or Major

Oceanography

Degree Name

Master of Science

First Advisor

Robert T Letscher

Second Advisor

Kai Ziervogel

Third Advisor

Elizabeth Harvey

Abstract

Marine microbes are vital to oceanic ecosystems and influence the global climate through their paramount role in Earth’s biogeochemical cycles. With this intricate role in ecosystems, it is important to understand the effect of increasing ocean temperatures on the cycling of organic matter (OM), which is hypothesized to contribute a positive feedback to future warming via an acceleration in microbial respiration of OM to CO2. We experimentally investigated the temperature sensitivity of microbial consumption of marine particulate OM focused in the rapidly warming Gulf of Maine during the 2019 and 2020 Fall phytoplankton bloom. The overall rate and quantity of microbial OM (C, N, and P pools) consumption at in situ versus elevated temperatures were quantified within bottle incubations over the course of two weeks. The results indicate that OM incubated at warmer temperatures (+5 – 6°C) was consumed at a faster rate with an overall larger quantity consumed compared to cooler temperatures (12 – 14°C). Additionally, nitrate that initially accumulated from the consumption of particulate organic nitrogen (PON), was readily consumed at later time points at both temperatures, possibly related to the carbon-rich, nitrogen-poor quality of the in situ OM. In 2020, more nitrogen-rich OM was preferentially consumed at cooler temperatures, leaving behind carbon-rich OM. Whereas at warmer temperatures, carbon-rich OM was preferentially consumed presumably due to it being a bioavailable energy source to fuel elevated metabolic rates. The empirically estimated temperature coefficient (Q10) ranged from 2.66 – 3.42 in 2019 versus 0.94 – 1.21 in 2020, dependent on the OM elemental pool, suggesting temperature plays an important role in OM consumption, but is not the only factor contributing to the rates and magnitude of OM consumption by marine microbes.

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