Biogeochemical cycling of dissolved zinc in the Indian Ocean

Abstract

Abstract We present the biogeochemical cycling of dissolved zinc (dZn) in marginal and open waters of the Indian Ocean using a high‐resolution dataset collected during multiple GEOTRACES‐India (GI) cruises. Atmospheric dust deposition is a minor source compared to continental shelf inputs for dZn in photic waters of the northern Indian Ocean. A strong linear relationship between dZn and silicate (Si) is noted across the Indian Ocean, with lower slope ratios (dZn : Si) in the Arabian Sea (0.045 ± 0.001 nM μ M −1 ) and Bay of Bengal (0.049 ± 0.001 nM μ M −1 ) relative to the southern tropical Indian Ocean (STIO, 0.062 ± 0.002 nM μ M −1 ). We investigated these regional differences using an inverse modeling approach by quantifying the fractional contribution of each water mass to the measured dZn concentrations in the water column. Our results indicate that water mass mixing and scavenging are the primary mechanisms controlling dZn distribution in the region. Scavenging of dZn in the intermediate waters is likely driving the lower dZn‐Si regression slopes in the northern Indian Ocean. Intense scavenging may result from zinc sulfide formation in anoxic microenvironments of poorly ventilated waters or adsorption onto sinking particles. Dissolved Zn in excess of its preformed component is nearly twice as high in deep waters of the northern Indian Ocean compared to the STIO, suggesting desorption of previously scavenged Zn and/or presence of regional deep sources. These findings advance our understanding of regional zinc cycling in the Indian Ocean.

Affiliated Institutions

• National Institute of Oceanography IN
• GEOMAR Helmholtz Centre for Ocean Research Kiel DE
• Rutgers, The State University of New Jersey US
• Physical Research Laboratory IN

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