Dissolved bio-essential metals in the Lazarev and Weddell Sea

During the 2018-2019 Antarctic summer season, shipboard measurements of dissolved iron (DFe) concentrations were made in the Lazarev and Weddell Sea and samples were collected for multi element analysis. Surface concentrations of Fe were depleted (<0.2 nM) throughout the region, even close to the continent. The exception was near the Antarctic Peninsula, but elevated surface concentrations did not persist far off shore. This is most likely due to a combination of precipitation and biological uptake. In the subsurface part of the water column, DFe concentrations were generally low offshore. Concentrations increased with depth but the highest concentrations remained around ~0.5 nM. Several bio-assay experiments were performed in both the open ocean and closer to shore. Measurements demonstrated that the dFe concentrations remained low throughout the experiments in the non-amended controls. The addition of iron improved the photosynthetic capacity, Fv/Fm, and had a profound effect on the amount of biomass and nutrient uptake in the off shore experiments, but less so in the near shore experiments. Besides Fe, the concentrations of Mn were low in the open ocean as well, and within two of the bio-assays, extremely low concentrations of Mn were observed. The other bio-essential metals did not appear to be fully depleted.