The distribution of reactive iron along the northeast Pacific margin and the delivery of this coastal iron to the open ocean

The objective of this dissertation is to characterize the distribution of reactive iron in the near-field Columbia River plume, the coastal Gulf of Alaska, and a Kenai eddy in the Gulf of Alaska (GoA). The research conducted for this dissertation presents a substantial contribution to the continuing effort to characterize the continental source of reactive iron and the delivery of that iron to the coastal ocean. Reactive iron is defined here as the sum of the leachable particulate and dissolved iron phases, and is an estimate of the total potentially bioavailable iron concentration. In the near-field Columbia River plume (Chapter 1), tidal amplitude and river flow were found to be the primary factors influencing the estuary leachable particulate Fe concentrations, with greater values during high flow and/or spring tides; resuspended shelf sediment was an additional source to the plume during coastal upwelling and spring tides. Leachable particulate iron concentrations in both the river/estuary and near-field plume were consistently one to two orders of magnitude greater than dissolved iron concentrations. Chapter 2 characterizes reactive iron concentrations in the Alaska Coastal Current. Coastal waters in the northern GoA are considered iron-rich and nitrate-poor, in contrast to the iron-poor, high-nitrate, low chlorophyll (HNLC) waters of the central GoA. The degree of mixing between these two regimes, is essential to maintain high productivity. Surface water leachable particulate iron concentrations were more variable and at least an order of magnitude higher than dissolved iron concentrations; the data suggests that the system's ability to solubilize this large concentration of leachable particulate iron is overwhelmed by the massive input of glacial-derived particulate iron. Chapter 3 discusses the delivery of this coastal iron to HNLC waters via a Kenai eddy. In the subsurface core of the eddy there was nearly nine times more reactive iron at inside eddy stations compared to the basin waters. Deep mixing can bring iron enriched eddy core waters to the surface and promote primary production. Furthermore, anticyclonic GoA eddies can be a source of iron to HNLC waters when they propagate into the central GoA and eventually relax or rebound.