Researcher ORCID Identifier

0009-0000-4105-0723

Graduation Year

2026

Date of Submission

12-2026

Document Type

Open Access Senior Thesis

Degree Name

Bachelor of Arts

Department

Environmental Analysis

Second Department

W.M. Keck Science Department

Reader 1

Branwen Williams

Reader 2

Veronica Vriesman

Terms of Use & License Information

Terms of Use for work posted in Scholarship@Claremont.

Rights Information

© 2025 Jesse I Dong

Abstract

Increasing anthropogenic carbon flux into the oceans decreases seawater pH, alters dissolved inorganic carbon speciation, and reduces biogenic calcification. The marine calcifiers— specifically corals and coralline algae—incorporate elements from surrounding seawater into their carbonate structures, which preserve past records of ocean carbon chemistry. In particular, boron in biogenic carbonate is a potentially valuable proxy for historical ocean pH across human timescales. Within seawater, boron primarily exists as boric acid B(OH)3 and borate ions B(OH)4 - , where higher pH favors the formation of borate ions. Borate ions preferentially incorporate the heavier ¹¹B isotope over 10B. On the other hand, if seawater pH decreases, boric acid forms, and the δ¹¹B of the borate declines. Because marine calcifiers intake borate as the source of boron in their skeletons, their δ¹¹B value reflects ambient seawater pH. However, available reconstructions do not capture the full temporal and spatial heterogeneity of seawater pH variability caused by anthropogenic activities. To address these gaps, ocean model outputs of seawater δ¹¹B can provide additional seawater pH data. Yet, there is little instrumental data to evaluate the ocean model output; comparisons between proxy reconstructions and model data are rare. Here, we use the Ocean Circulation Inverse Model with a biogeochemical component (OCIM2-BGC)—a data-assimilated transport matrix model that simulates the transient carbon cycle from 1750 to the present, assuming a climatological mean ocean circulation. Through an inverse modeling approach, seawater pH and δ¹¹B are calculated using dissolved inorganic carbon and alkalinity output from OCIM2-BGC. Comparison of OCIM-modeled δ¹¹B with published marine calcifier δ¹¹B reconstructions provides a clearer picture of historical ocean pH. By doing so, we can quantify model and reconstruction reliability to more concretely understand global ocean carbon chemistry.

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