DETERMINING WHETHER IRON IS A LIMITING IN THE GULF OF MAINE

Trace metals, including iron, play a role in the distribution and productivity of phytoplankton. Iron is found in relatively low concentrations in saltwater systems, due to its low solubility. Previous studies have quantified Fe availability and found it may be a limiting nutrient in the summer in the North Atlantic, but no recent measurements within the Gulf of Maine have been made with trace metal clean sampling. Over two cruises in June and July 2024, we measured dissolved and particulate iron and macronutrients (nitrate+nitrite, phosphate, and silicate) at 15 m at 3 stations along a horizontal transect, and depth profiles at 2 of the stations. Seawater was filtered through a 0.4 um cartridge filter (Acropak) at sea and then acidified with trace metal grade HCl for analysis of dissolved iron. Whole seawater was filtered through a 0.4 um polycarbonate filter and halved for total and labile particulate iron analysis. Inductively coupled plasma mass spectroscopy (ICP-MS) was used to quantify iron and phosphorus concentrations. Macronutrients were measured using standard autoanalyzer methods. Dissolved and particulate iron was lower offshore away from river input and higher toward the benthic layer. Particulate labile Fe/P in reference to phytoplankton stoichiometry of cells showed a large abiotic source of labile Fe that increased with depth. Refractory Fe/Al conclude that iron is enriched over aluminum in comparison to the average crustal values. The dissolved N/Fe values were below 10 mol/mmol, suggesting nitrogen limitation before an iron limitation for surface values.

Presentation Preference: Poster

Primary Presenter: Kayla Ellerbe, University of Miami (kaylaellerbe@gmail.com)

Authors:

Kayla Ellerbe, University of MIami  (kaylaellerbe@gmail.com)

Laura Sofen, Bigelow Laboratory for Ocean Sciences  (lsofen@bigelow.org)

Benjamin Twining, Bigelow Laboratory for Ocean Sciences  (btwining@bigelow.org)

Jarret Mayo, Bigelow Laboratory for Ocean Sciences  (jmayo@bigelow.org)