UC San Diego

Iron and copper are essential bioactive elements in the marine environment, but they have a complex chemical speciation dominated by a heterogeneous mixture of organic metal-ligand complexes. Numerous analytical constraints complicate the direct chemical characterization of these species, thus this work seeks to expand upon existing indirect electrochemical methods for examining copper and iron organic complexes in seawater. A multiple analytical window (MAW) electrochemical approach, which enables the detection of a broad spectrum of ligands, is applied in new regions of the ocean for copper and, for the first time, in studies of iron speciation. Chapter 2 describes the first application of the MAW electrochemical technique for copper speciation in the open ocean. Copper-binding ligands were measured in four surface water masses of the Antarctic Peninsula region, and each water mass was shown to contain distinct pools of ligands. Chapters 3 and 4 focus on applying the MAW electrochemical method to iron- binding ligands. In Chapter 3, iron-binding ligands were measured in central California coastal waters in the surface and benthic boundary layer (BBL), in order to validate the MAW approach for iron speciation in contrasting chemical regimes. Iron-binding ligands in surface waters were found to be chemically distinct from the BBL ligand pool. Chapter 4 explores San Francisco Bay as a source of iron-binding ligands to coastal California waters. Scavenging in the estuary caused the concentration of weaker ligands to decrease with salinity, while the strongest ligands remained largely resistant to flocculation. Chapter 5 applies the MAW electrochemical technique in experimental studies and water column profiles to interpret mechanisms of in-situ iron-binding ligand cycling in the southern California Current. Photochemical processes were found to dominate in near surface waters, while biological processes controlled ligand distributions in deeper waters. Overall, the simultaneous detection of multiple ligand classes has contributed significantly to our existing knowledge of metal ligand sources and sinks, and the unique chemical environments in which phytoplankton are utilizing trace nutrients