Geochemical and physical processes influencing the composition of particles in diverse environments, eastern North Atlantic Ocean

• Main Author: Isley, Ann Elaine
• Format: Text
• Language: English
• Published: DigitalCommons@URI 1990
• Subjects: Geochemistry|Geology|Mineralogy; Mid-Atlantic Ridge; North Atlantic
• Online Access: https://digitalcommons.uri.edu/dissertations/AAI9109466

To understand global biogeochemical cycling in the oceans it is imperative to develop comprehensive models of the processes influencing elements in the suspended particulate phase. This thesis examines the character of particles from a wide variety of environments in the Eastern North Atlantic Ocean in order: (1) to enhance our knowledge of the physical and geochemical processes influencing resuspended matter; (2) to determine over what distances distinct water masses can transport characteristic particle suites; (3) to develop models for the formation and transformation of distinct mineral phases associated with hydrothermal plumes. Particles were collected by filtering water from 30 liter Niskin bottles and by using in situ high-volume filtration equipment during the FLUXATLANTE (R/V Suroi t, 1985) and RRS Discovery 159 (1986) cruises. Particles were characterized using some or all of the following techniques: instrumental neutron activation (for Al, Ca, Fe, Mn, Cu, V, and/or I), scanning electron microscopy and energy dispersive x-ray analyses. Differences between resuspended nepheloid materials and underlying surface sediments are attributed to preferential resuspension of fine-grained materials with a distinctive geochemical signature. Classical signs of early alteration processes such as dissolution of biogenic tests and remineralization of organic matter in the sediment column are observed. Long-distance transport (to 800 km) of aluminosilicates occurs with advection of Mediterranean Outflow Water (MEDW). Mixing with Eastern North Atlantic Intermediate Water (ENAIW) accounts for an enhanced particulate Ca/Al and Mn/Al in intermediate waters with distance from Gibraltar and there is no evidence for adsorption of dissolved Mn introduced with the MEDW plume over distance scales $\approx$1000 km. Between 15 to 75% of the materials transported in the Trans-Atlantic Geotraverse hydrothermal plume (26$\sp\circ$N, Mid-Atlantic Ridge) are of resuspended origin. Hydrothermal particles are dominated by amorphous iron oxides along the length of the equilibrated plume. Copper oxides are present in the region of 2.5 km from the venting site. Manganese-rich particles are introduced to the plume via resuspension. Sulfides may be transported into the far-field hydrothermal plume only if their grain sizes are $<$3 $\mu$.