Date of Award

Spring 1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean & Earth Sciences

Program/Concentration

Oceanography

Committee Director

Gregory A. Cutter

Committee Member

G. Wong

Committee Member

Eileen Hofmann

Committee Member

William Landing

Abstract

Hydrogen sulfide is a poorly quantified component of the global sulfur cycle. In seawater, its dissolved species (dissolved sulfide) can react with trace metals to form dissolved complexes and insoluble compounds. Therefore, the study of dissolved° sulfide in the open ocean can yield a better understanding of the biogeochemical cycles of sulfur and trace metals.

The biogeochemical cycling of dissolved sulfide was examined using specially developed sampling and analytical methods. In the western North Atlantic and central Equatorial Pacific Oceans, total dissolved sulfide concentrations ranged from /L; they were highest, in the mixed layer and decreased with depth. The depth distribution and the rate of carbonyl sulfide (OCS) hydrolysis to hydrogen sulfide under oceanographic condition were determined because of their importance for the cycling of dissolved sulfide. Depth profiles of OCS show near-surface enrichment up to 150 pmol/1, and depletion at depth. These profiles suggest in situ OCS production, perhaps by organic matter regeneration. A budget was constructed to quantify the sources and sinks of dissolved sulfide in the Sargasso Sea mixed layer. The rate of dissolved sulfide production was 5.43 pmol/L/h (OCS hydrolysis + air/sea exchange), a.ncl the removal rate was 115.2 pmol/1/h (oxidation+ particulate sinking). Similarities in profiles of dissolved sulfide and chlorophyll a or Synechococcus sp., and results from recent phytoplankton culture studies, also suggest its production by phytoplankton; this source is necessary to balance the dissolved sulfide budget.

The conditional formation constant of Cu(HS)+ was determined under oceanographic conditions and is 109.1± 0.6. The speciation of dissolved sulfide was computed with this constant and literature thermodynamic data using a multiequilibrium model. The calculation predicts that 80% of dissolved sulfide is uncomplexed in the mixed layer, while over 90% is complexed by zinc and copper below the pycnocline. Because dissolved sulfide is rapidly cycled and interact.s with Irace met.a.ls, future studies should continue to quantify, under oceanographic conditions, its the interactions with trace meta.ls, and its rat.e of product.ion by phytoplankton.

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DOI

10.25777/03qq-f873

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