Dissolved Scandium and Iron in the Ocean: an investigation into the potential use of scandium distributions and into a new region of iron limitation
The objective of this dissertation was to expand upon the very different states of knowledge of dissolved scandium (Sc) and iron (Fe) in the ocean. Iron is highly-studied and important biologically as an essential and often limiting micronutrient, yet characterizing the cycling of Fe fully has proved challenging. Scandium, in contrast, has barely been studied in the ocean prior to this dissertation, yet upon investigation reveals potentially useful attributes including the possibility of shedding some light on the oceanic Fe cycle. The first chapter of this dissertation characterizes the distribution and reactivity of dissolved Sc by comparing deep-water Atlantic to Pacific concentration ratios of Sc with other, better characterized Group IIIA and IIIB trivalent metals: yttrium (Y), lanthanum (La), gallium (Ga), and aluminum (Al). Results indicate that Sc is a hybrid-type metal, more particle reactive than Y and La in Group IIIB and less particle reactive than Ga and Al in Group IIIA, with an inferred oceanic residence time on the order of 1000 years. Results also suggest that Sc may represent the non-nutrient side of the oceanic Fe cycle. Chapter 2 investigates the potential to use the particle reactivity difference between Sc and its periodic table group-mates Y and La to give an indication of scavenging intensity. Results indicate that Sc, Y and La are input to the surface North Atlantic Ocean in relatively constant ratios compared with the dissolved ratios, suggesting that the variations in the dissolved ratios are due to Sc removal through scavenging. Dissolved Y/Sc and La/Sc ratios correlate well with the shape of the gyre, suggesting that they may be driven by and provide indication of export production. Chapter 3 brings the story back to Fe with an investigation of Fe-limitation of coastal diatoms off the coast of southern Oregon. There are many studies demonstrating Fe-limitation off the California coast, but so far the Oregon coastline had only been shown to have elevated Fe from the Columbia River. Results from Chapter 3 provide evidence for Fe-limitation of growth rate and biomass accumulation of coastal diatoms off the southern Oregon coast near Cape Blanco, indicating that the Fe-limitation mosaic extends further north than previously known.