Department or Program
Earth and Climate Sciences
Second Department or Program
Biochemistry
Abstract
The ecosystem found within Gulf of Maine is both economically valuable, and rapidly changing. It is important to study past hydrographic and ecosystem changes to understanding how the system may behave in the future. This can be done by utilizing stable nitrogen isotopes from paleomarine organism’s tissue. Previous nitrogen isotope studies of bulk proteins extracted from ancient Atlantic cod (Gadus morhua) tissues document a 1-2‰ decrease in δ15N values over the last couple of centuries (Harris et al., unpub; Lueders-Dumont et al., 2018). Due to the nature of the nitrogen isotope signal in bulk proteins, this isotopic shift may be attributed to a decrease in trophic level and/or a change in baseline nitrogen in the Gulf of Maine over this time period. Here, we analyze the δ15N value of individual amino acids (AA) from ancient cod bone collagen to tease out the relative importance of shifts in trophic level vs baseline nitrogen sources to cod diets through time. The δ15N values of phenylalanine (minimally-fractionating “source” amino acid) extracted from cod bone collagen fluctuated between 4.8±0.9‰ to 9.4±1.3‰ over the last 4,400 years with a peak at 500 yr BP. This peak in δ15NPhe suggests a shift in basal nitrogen sources, potentially linked to changes in hydrographic conditions, such as an increased influence of Labrador Slope Water during this period. The calculated trophic position (TP) shows a significant decline at 500 years BP, which may be associated with the pulse of Labrador Slope Water (LSW). This pulse of LSW could have impacted the ecosystem by shortening the food web or by triggering changes in indigenous fishing practices that favored smaller cod.
Level of Access
Restricted: Embargoed [Bates Community After Expiration]
First Advisor
Johnson, Beverly
Date of Graduation
5-2025
Degree Name
Bachelor of Science
Recommended Citation
Turtle, Samantha L., "Using CSIA-AA of Paleo Cod Bone Collagen to Uncover Changes in Basal Nitrogen Sources and Trophic Position in the Gulf of Maine Over the Past 4,400 Years" (2025). Honors Theses. 485.
https://scarab.bates.edu/honorstheses/485
Number of Pages
81
