Investigating seasonal trends in dissolved iron-binding organic ligands in the BATS region of the North Atlantic Ocean

Salvatore Caprara1, Bettina M Sohst2, Rodney Johnson3, Daniel Ohnemus4, Alessandro Tagliabue5, Benjamin S Twining6, Peter Sedwick2 and Kristen N Buck1, (1)University of South Florida, College of Marine Science, Saint Petersburg, FL, United States, (2)Old Dominion University, Department of Ocean, Earth and Atmospheric Sciences, Norfolk, VA, United States, (3)Bermuda Institute of Ocean Sciences, St. George's, Bermuda, (4)Skidaway Institute of Oceanography, Savannah, GA, United States, (5)University of Liverpool, Liverpool, United Kingdom, (6)Bigelow Lab for Ocean Sciences, East Boothbay, ME, United States
Marine primary production is strongly influenced by the availability of iron, an essential micronutrient. Organic iron-binding ligands are increasingly recognized to play a governing role in the bioavailability and associated biogeochemical cycling of iron in seawater. The GEOTRACES program has facilitated recent high-resolution datasets of the characteristics and distributions of iron-binding ligands across ocean basins, which highlight the ubiquity of these ligands in ocean water columns. Temporal changes in iron-binding ligands in the upper ocean, including how seasonal changes in mixing and productivity influence open ocean iron speciation, remain unresolved. To assess this, iron-binding organic ligands were measured by competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV) in water-column samples collected from the Bermuda Atlantic Time-series Study (BATS) region of the western subtropical North Atlantic, the location of a long running open ocean biogeochemistry time-series and a designated baseline station for the international GEOTRACES program. Samples for dissolved (< 0.2 µm) iron-binding organic ligands were collected from the upper 2,000 m, during three BATS cruises (March, May and August 2019) as part of the BAIT (Bermuda Atlantic Iron Time-series) project. All samples were collected using trace metal clean sampling techniques and analyzed by CLE-AdCSV at the University of South Florida. Additional samples for soluble (<0.02 µm) iron-binding organic ligands were collected from the mixed layer of each depth profile. These data offer insight into seasonal trends in iron speciation in a well-studied open ocean system.