Graduation Year

2024

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Marine Science

Major Professor

Kristen N. Buck, Ph.D.

Co-Major Professor

Mya Breitbart, Ph.D.

Committee Member

Robert H. Byrne, Ph.D.

Keywords

trace metals, biogeochemistry, North Atlantic, bioavailability, ligands

Abstract

Here I present the first depth profiles of dissolved nickel (DNi) speciation over an annual cycle at the Bermuda Atlantic Time-series Study (BATS) site in the North Atlantic. Seawater samples were collected in March, May, August, and November 2019 and analyzed for labile DNi using competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV). Labile DNi was measured by CLE-AdCSV as the fraction of DNi that exchanges with an added competitive ligand in an overnight equilibration. Results revealed two distinct fractions of DNi present throughout the water column: a labile fraction, and a strongly organically complexed (i.e., non-labile) fraction. More than 50% of the total DNi was labile across all depths and seasons sampled, suggesting that most of the DNi in the BATS water column is bioavailable. Local maxima of DNi and labile DNi in near-surface waters may indicate a source of Ni to the euphotic zone, and an increasing proportion of non-labile DNi with depth suggests either potential exchanges between labile and organically complexed forms of DNi or distinct preformed Ni speciation in advected water masses. Results also suggest that interactions with manganese (Mn) may be important drivers of DNi and labile DNi distributions through the water column. Speciation measurements are a valuable tool for uncovering processes affecting trace metal distributions and bioavailability. These results provide novel insights into DNi biogeochemical dynamics in the North Atlantic.

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