Iron (Fe) is an essential micronutrient for primary production but is often present at low concentrations (<0.1 nM), limiting primary production and nitrogen fixation over vast regions of the surface ocean. Dissolved Fe (dFe) is routinely elevated (up to 10 nM) in waters overlying the West Florida shelf, yet the relative importance of key dFe sources remains unclear. Dissolved Fe isotopic compositions (δ⁵⁶Fe) are a valuable oceanographic tool for identifying sources and internal cycling of dFe in the global ocean. The δ⁵⁶Fe endmembers of key Fe sources to the surface ocean are well established, but limitations on spatial and temporal data leaves a high degree of uncertainty in the global riverine δ⁵⁶Fe endmember (-1.34 to +1.78‰). Across the estuarine transition, removal processes such as flocculation, scavenging and precipitation facilitate significant loss of riverine Fe from the dissolved phase and are associated with a high degree of Fe isotopic fractionation. Here we present dFe and δ⁵⁶Fe data from five key rivers (Hillsborough, Alafia, Manatee, Peace, Caloosahatchee) three estuaries (Tampa Bay, Charlotte Harbor and Caloosahatchee Estuary) and eleven submarine groundwater wells on the West Florida Shelf to investigate the relative importance of such Fe sources to the shelf environment. We aim to further constrain mechanisms of modification, addition, or removal of dFe through the riverine-estuarine-open ocean transition in this region, with implications for understanding the role of riverine derived Fe on primary production, nitrogen fixation, and red tide. 

Primary Presenter: Hannah Hunt, University of South Florida (hannahhunt@usf.edu)

Authors:

Rene Boiteau, Oregon State University  (rene.boiteau@oregonstate.edu)

Kristen Buck, Oregon State University  (kristen.buck@oregonstate.edu)

Salvatore Caprara, University of South Florida  (caprara@mail.usf.edu)

P. Dreux Chappell, Old Dominion University  (pdchappe@odu.edu)

Emily Hall, Mote Marine Laboratory  (emily8@mote.org)

Katherine Hubbard, Fish and Wildlife Research Institute  (katherine.hubbard@myfwc.com)

Angela Knapp, Florida State University  (anknapp@fsu.edu)

Christopher Smith, USGS  (cgsmith@usgs.gov)

Joseph Tamborski, Old Dominion University  (jtambors@odu.edu)

Timothy Conway, University of South Florida  (tmconway@usf.edu)