The Marine Biogeochemistry of Trace Metals

• Main Author: Roshan, Saeed
• Other Authors: Jingfeng Wu, Frank J. Millero, Dennis A. Hansell, Larry E. Brand
• Format: Other/Unknown Material
• Language: unknown
• Published: Scholarly Repository 2016
• Subjects: trace metals; dissolved iron; dissolved manganese; dissolved zinc; dissolved copper; dissolved cadmium; Pacific; Southern Ocean; North Atlantic
• Online Access: https://scholarlyrepository.miami.edu/oa_dissertations/1684; https://scholarlyrepository.miami.edu/cgi/viewcontent.cgi?article=2699&context=oa_dissertations

Some of the transition metals play major roles within the biology of the ocean, but occur in the ocean at the “trace” levels of concentration. They, particularly, function in the metabolism and thriving of the marine primary producers which contribute significantly to the global photosynthesis and are the base of the marine food web. Iron (Fe), zinc (Zn), copper (Cu), cadmium (Cd), and manganese (Mn) are among the most important trace metals whose oceanic behavior in terms of distribution, cycling, sources, sinks, and similarities to macronutrients such as phosphate (PO4 3-), nitrate (NO3 -), and silicate (SiO4 4-) are studied in this dissertation. The data produced during this dissertation are considered as an outcome of the GEOTRACES program (www.geotraces.org). These studies have been conducted in the tropical-subtropical North Atlantic and the tropical South Pacific. The dissolved Zn distribution was determined in the North Atlantic and the South Pacific. The North Atlantic’s distribution shows decoupling with SiO4 4- which is in contrast to the previous studies that have demonstrated tight correlations between these two species within the ocean. Using a novel multi-endmember modeling, it was shown that dissolved Zn in the North Atlantic is mainly controlled by mixing and the decoupling with SiO4 4- is due to decoupling in the upstream endmembers. Dissolved Zn shows a remarkable enrichment in the deep South Pacific in correspondence to helium-3 (3He), which is a tracer of hydrothermal activity. The global flux of dissolved Zn estimated from the observations are many times higher than the fluvial and dust input. Analysis of the dissolved Cd distribution in the North Atlantic shows that dissolved Cd in the upper 1000 m is mainly controlled by remineralization process, whilst Cd in the deeper water columns is mainly controlled by water mass mixing. This indicates that Cd incorporated in the benthic forams sampled below 1000 m can be attributed to the plaeo water masses. In the tropical South Pacific, dissolved Cd shows a significant decoupling with PO4 3- which is coincident with the low-SiO4 4- waters, indicating a role for Felimitation in the Southern Ocean in modulating the Cd-PO4 3- relationship, given that Felimitation results in higher Cd/P ratio in diatoms. The dissolved Cu distribution in the North Atlantic displays a significant accumulation in the deep water column, near the seafloor. On the other hand, it also correlates with SiO4 4- with a higher Cu/SiO4 4- than the Southern Ocean, indicating an input from the seafloor sediments. Similar to dissolved Zn, dissolved Fe and Mn show an enrichment emanating from the EPR. Size-partitioning experiment shows that most of hydrothermal dissolved Fe is fractionated into the macro-colloids (>300 kDa), whilst the hydrothermal dissolved Mn is totally found in very small species (<5 >kDa). This indicates the contrasting geochemistry of these two elements.